we have grown our total revenue from $ 209.6 million in 2014 to $ 445.6 million in 2018. during this period , our operating expenses increased from $ 67.9 million in 2014 to $ 149.8 million in 2018. we have grown our income from operations from $ 60.5 million in 2014 to $ 88.9 million in 2018. our recent growth in revenue and income from operations has been accompanied by increased cost of revenues and operating expenses . we expect to increase investment in our operations to support anticipated future growth as discussed more fully below . in addition , we believe that a number of trends affecting our industry have affected our results of operations and may continue to do so . for example , we believe that many of our target product developer and engineer customers are facing three mega trends , which are disrupting product growth models . we believe our customers are facing increased pressure to shorten product life-cycles , to embed products with internet of things technology , and to deliver products that are personalized and customized to unique customer specifications . we believe we continue to be well positioned to benefit from these trends , given our proprietary technology that enables us to automate and integrate the majority of activities involved in procuring custom parts . while our business may be positively affected by these trends , our results may also be favorably or unfavorably impacted by other trends that affect product developer and engineer orders for custom parts in low volumes , including , among others , changes in product developer and engineer preferences or needs , developments in our industry and among our competitors , and factors impacting new product development volume such as economic conditions . for a more complete discussion of the risks facing our business , see part i , item 1a . “ risk factors ” of this annual report on form 10-k. 32 key financial measures and trends revenue our operations are comprised of three geographic operating segments in the united states , europe and japan . revenue is derived from our injection molding , cnc machining , 3d printing and sheet metal product lines . injection molding revenue consists of sales of custom injection molds and injection-molded parts . cnc machining revenue consists of sales of cnc-machined custom parts . 3d printing revenue consists of sales of 3d-printed parts . sheet metal revenue consists of sales of fabricated sheet metal custom parts . our revenue is generated from a diverse customer base , with no single customer company representing more than 2 % of our total revenue in 2018. our historical and current efforts to increase revenue have been directed at gaining new customers and selling to our existing customer base by increasing marketing and selling activities , including : the introduction of our 3d printing product line through our acquisition of fineline in 2014 ; expanding 3d printing to europe through our acquisition of alphaform in october 2015 ; the introduction of our sheet metal product line through our acquisition of rapid in 2017 ; continuously improving the usability of our product lines such as our web-centric applications ; and expanding the breadth and scope of our products by adding more sizes and materials to our offerings . during 2018 , we served 45,968 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 22.5 % over the same period in 2017. during 2017 , we served 37,538 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 19.3 % over the same period in 2016. during 2016 , we served 31,457 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 15.5 % over the same period in 2015. the 2016 information does not include 3d printing and injection molding customers resulting from the alphaform acquisition who do not utilize our web-based interface . cost of revenue , gross profit and gross margin cost of revenue consists primarily of raw materials , equipment depreciation , employee compensation , benefits , stock-based compensation , facilities costs and overhead allocations associated with the manufacturing process for molds and custom parts . we expect cost of revenue to increase in absolute dollars , but remain relatively constant as a percentage of total revenue . our business model requires that we invest in our capacity well in advance of demand to ensure we can fulfill the expectations for quick delivery of our products to our customers . therefore , during each of 2018 , 2017 and 2016 we made significant investments in additional factory space , equipment , and infrastructure in the united states . we also made significant investments in infrastructure in europe in 2017 and significant investments in additional factory space in japan in 2016. we expect to continue to grow in future periods , which will result in the need for additional investments in factory space and equipment . we expect that these additional costs for factory and equipment expansion can be absorbed by revenue growth , and allow gross margins by product line to remain relatively consistent over time . we define gross profit as our revenue less our cost of revenue , and we define gross margin as gross profit expressed as a percentage of revenue . our gross profit and gross margin are affected by many factors , including our mix of revenue by product line , pricing , sales volume and manufacturing costs , the costs associated with increasing production capacity , the mix between domestic and foreign revenue sources and foreign exchange rates . 33 operating expenses operating expenses consist of marketing and sales , research and development and general and administrative expenses . personnel-related costs are the most significant component in each of these categories . story_separator_special_tag replace_table_token_11_th 39 liquidity and capital resources cash flows the following table summarizes our cash flows for the years ended december 31 , 2018 , 2017 and 2016 : replace_table_token_12_th story_separator_special_tag million in proceeds from exercises of stock options . cash provided by financing activities was $ 9.2 million for the year ended december 31 , 2017 , consisting of $ 5.0 million in short-term debt obligations and $ 8.6 million in proceeds from the exercise of stock options , partially offset by $ 4.4 million for repurchases of common stock . cash provided by financing activities was $ 5.3 million for the year ended december 31 , 2016 , consisting of $ 5.7 million in proceeds from exercises of stock options , partially offset by $ 0.4 million for payments of acquisition-related contingent consideration . operating and capital expenditure requirements we believe , based on our current operating plan , that our cash balances and cash generated through operations and interest income will be sufficient to meet our anticipated cash requirements through at least the next 12 months . from time to time we may seek to sell equity or convertible debt securities or enter into credit facilities . the sale of equity and convertible debt securities may result in dilution to our shareholders . if we raise additional funds through the issuance of convertible debt securities or enter into credit facilities , these securities and debt holders could have rights senior to those of our common stock , and this debt could contain covenants that would restrict our operations . we may require additional capital beyond our currently forecasted amounts . any such required additional capital may not be available on terms acceptable to us , or at all . our future capital requirements will depend on many factors , including the following : the revenue growth in injection molding , cnc machining , 3d printing and sheet metal product lines ; costs of operations , including costs relating to expansion and growth ; the emergence of competing or complementary technological developments ; the costs of filing , prosecuting , defending and enforcing any patent claims and other intellectual product rights , or participating in litigation-related activities ; and the acquisition of businesses , products and technologies , although we currently have no commitments or agreements relating to any of these types of transactions . our recent annual capital expenditures have varied between 10 % and 20 % of annual revenue . we believe future growth capital expenditures , excluding any expenditures for buildings and maintenance capital we might purchase for our operations , are likely to vary between approximately 8 % and 12 % of annual revenue . 41 contractual obligations as of december 31 , 2018 , our contractual obligations and the effect such obligations are expected to have on our liquidity and cash flows in future periods were as follows : replace_table_token_13_th the table above reflects only payment obligations that are fixed and determinable . our commitments for operating leases relate to three of our united states manufacturing facilities ; our european sales , customer service and technical support offices ; manufacturing and office facilities located in germany ; and our japan facility . financing arrangements the following table summarizes our financing arrangements as of december 31 , 2018 and 2017 : december 31 , ( in thousands ) 2018 2017 revolving credit facility , with interest rates from 2.50 % to 2.59 % , due at maturity in november 2019 $ - $ 5,000 total financing obligations $ - $ 5,000 inflation we experience normal inflation and changing prices , primarily on our production materials and labor . we believe that inflation and changing prices have not had a material effect on our financial condition during the three most recent fiscal years . off-balance sheet arrangements since our inception , we have not engaged in any off-balance sheet arrangements , including the use of structured finance , special purpose entities or variable interest entities . critical accounting policies and use of estimates the discussion and analysis of our financial condition and results of operations is based upon our consolidated financial statements , which have been prepared in accordance with accounting principles generally accepted in the united states . the preparation of these financial statements requires us to make estimates , judgments and assumptions that affect the reported amount of assets , liabilities , revenue , expenses and related disclosures . on an ongoing basis , we evaluate our estimates , including those related to revenue recognition , goodwill , other intangible assets , stock-based compensation , and income taxes . we base our estimates of the carrying value of certain assets and liabilities on historical experience and on various other assumptions that we believe to be reasonable under the circumstances . in many cases , we could reasonably have used different accounting policies and estimates . in some cases , changes in the accounting estimates are reasonably likely to occur from period to period . management has discussed the development , selection and disclosure of these estimates with the audit committee of our board of directors . our actual results may differ significantly from these estimates under different assumptions or conditions . we believe the following critical accounting policies affect our more significant judgments used in the preparation of our consolidated financial statements . see the notes to consolidated financial statements included in item 8 . “ financial statements and supplementary data ” in this annual report on form 10-k for additional information about these critical accounting policies , as well as a description of our other accounting policies . 42 revenue recognition on january 1 , 2018 , we adopted asc 606 , revenue from contracts with customers , using the modified retrospective approach . we manufacture custom parts to specific customer orders that have no alternative use to us , and we believe there is a legally enforceable right to payment for performance

sources of liquidity we finance our operations and capital expenditures through cash flow from operations . we had cash and cash equivalents of $ 85.0 million as of december 31 , 2018 , an increase of $ 48.3 million from december 31 , 2017. the increase in our cash was due primarily to cash generated through operations . we had cash and cash equivalents of $ 36.7 million as of december 31 , 2017 , a decrease of $ 32.1 million from december 31 , 2016. the decrease in our cash was due primarily to the acquisition of rapid in november 2017. we had cash and cash equivalents of $ 68.8 million as of december 31 , 2016 , an increase of $ 21.1 million from december 31 , 2015. the increase in our cash was due primarily to cash generated through operations . as of december 31 , 2018 , the amount of cash and cash equivalents held by foreign subsidiaries was $ 46.9 million . the tax cuts and jobs act imposes a transition tax on foreign earnings previously treated as permanently reinvested , resulting in an increase to our u.s. tax liability . however , our intent is to continue to permanently reinvest these funds outside the u.s. and our current plans do not demonstrate a need to repatriate them to fund our domestic operations . we believe that our existing cash and cash equivalents together with cash generated from operations will be sufficient to meet our working capital expenditure requirements for at least the next 12 months . cash flows from operating activities cash flow from operating activities of $ 122.9 million during 2018 primarily consisted of net income of $ 76.6 million , adjusted for certain non-cash items , including depreciation and amortization of $ 26.8 million , stock-based compensation expense of $ 10.9 million and deferred taxes of $ 11.9 million , which were partially offset by changes in operating assets and liabilities and other items totaling $ 3.3 million .


 Write a concise suspicious activity report of the following text delimited by triple backquotes. Return your response as a formal report which covers the key points highlighting the location,dates,entity names and account holder information in chronological order of the text.
     ```sources of liquidity we finance our operations and capital expenditures through cash flow from operations . we had cash and cash equivalents of $ 85.0 million as of december 31 , 2018 , an increase of $ 48.3 million from december 31 , 2017. the increase in our cash was due primarily to cash generated through operations . we had cash and cash equivalents of $ 36.7 million as of december 31 , 2017 , a decrease of $ 32.1 million from december 31 , 2016. the decrease in our cash was due primarily to the acquisition of rapid in november 2017. we had cash and cash equivalents of $ 68.8 million as of december 31 , 2016 , an increase of $ 21.1 million from december 31 , 2015. the increase in our cash was due primarily to cash generated through operations . as of december 31 , 2018 , the amount of cash and cash equivalents held by foreign subsidiaries was $ 46.9 million . the tax cuts and jobs act imposes a transition tax on foreign earnings previously treated as permanently reinvested , resulting in an increase to our u.s. tax liability . however , our intent is to continue to permanently reinvest these funds outside the u.s. and our current plans do not demonstrate a need to repatriate them to fund our domestic operations . we believe that our existing cash and cash equivalents together with cash generated from operations will be sufficient to meet our working capital expenditure requirements for at least the next 12 months . cash flows from operating activities cash flow from operating activities of $ 122.9 million during 2018 primarily consisted of net income of $ 76.6 million , adjusted for certain non-cash items , including depreciation and amortization of $ 26.8 million , stock-based compensation expense of $ 10.9 million and deferred taxes of $ 11.9 million , which were partially offset by changes in operating assets and liabilities and other items totaling $ 3.3 million .
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 Suspicious Activity Report : we have grown our total revenue from $ 209.6 million in 2014 to $ 445.6 million in 2018. during this period , our operating expenses increased from $ 67.9 million in 2014 to $ 149.8 million in 2018. we have grown our income from operations from $ 60.5 million in 2014 to $ 88.9 million in 2018. our recent growth in revenue and income from operations has been accompanied by increased cost of revenues and operating expenses . we expect to increase investment in our operations to support anticipated future growth as discussed more fully below . in addition , we believe that a number of trends affecting our industry have affected our results of operations and may continue to do so . for example , we believe that many of our target product developer and engineer customers are facing three mega trends , which are disrupting product growth models . we believe our customers are facing increased pressure to shorten product life-cycles , to embed products with internet of things technology , and to deliver products that are personalized and customized to unique customer specifications . we believe we continue to be well positioned to benefit from these trends , given our proprietary technology that enables us to automate and integrate the majority of activities involved in procuring custom parts . while our business may be positively affected by these trends , our results may also be favorably or unfavorably impacted by other trends that affect product developer and engineer orders for custom parts in low volumes , including , among others , changes in product developer and engineer preferences or needs , developments in our industry and among our competitors , and factors impacting new product development volume such as economic conditions . for a more complete discussion of the risks facing our business , see part i , item 1a . “ risk factors ” of this annual report on form 10-k. 32 key financial measures and trends revenue our operations are comprised of three geographic operating segments in the united states , europe and japan . revenue is derived from our injection molding , cnc machining , 3d printing and sheet metal product lines . injection molding revenue consists of sales of custom injection molds and injection-molded parts . cnc machining revenue consists of sales of cnc-machined custom parts . 3d printing revenue consists of sales of 3d-printed parts . sheet metal revenue consists of sales of fabricated sheet metal custom parts . our revenue is generated from a diverse customer base , with no single customer company representing more than 2 % of our total revenue in 2018. our historical and current efforts to increase revenue have been directed at gaining new customers and selling to our existing customer base by increasing marketing and selling activities , including : the introduction of our 3d printing product line through our acquisition of fineline in 2014 ; expanding 3d printing to europe through our acquisition of alphaform in october 2015 ; the introduction of our sheet metal product line through our acquisition of rapid in 2017 ; continuously improving the usability of our product lines such as our web-centric applications ; and expanding the breadth and scope of our products by adding more sizes and materials to our offerings . during 2018 , we served 45,968 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 22.5 % over the same period in 2017. during 2017 , we served 37,538 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 19.3 % over the same period in 2016. during 2016 , we served 31,457 unique product developers and engineers who purchased our products through our web-based customer interface , an increase of 15.5 % over the same period in 2015. the 2016 information does not include 3d printing and injection molding customers resulting from the alphaform acquisition who do not utilize our web-based interface . cost of revenue , gross profit and gross margin cost of revenue consists primarily of raw materials , equipment depreciation , employee compensation , benefits , stock-based compensation , facilities costs and overhead allocations associated with the manufacturing process for molds and custom parts . we expect cost of revenue to increase in absolute dollars , but remain relatively constant as a percentage of total revenue . our business model requires that we invest in our capacity well in advance of demand to ensure we can fulfill the expectations for quick delivery of our products to our customers . therefore , during each of 2018 , 2017 and 2016 we made significant investments in additional factory space , equipment , and infrastructure in the united states . we also made significant investments in infrastructure in europe in 2017 and significant investments in additional factory space in japan in 2016. we expect to continue to grow in future periods , which will result in the need for additional investments in factory space and equipment . we expect that these additional costs for factory and equipment expansion can be absorbed by revenue growth , and allow gross margins by product line to remain relatively consistent over time . we define gross profit as our revenue less our cost of revenue , and we define gross margin as gross profit expressed as a percentage of revenue . our gross profit and gross margin are affected by many factors , including our mix of revenue by product line , pricing , sales volume and manufacturing costs , the costs associated with increasing production capacity , the mix between domestic and foreign revenue sources and foreign exchange rates . 33 operating expenses operating expenses consist of marketing and sales , research and development and general and administrative expenses . personnel-related costs are the most significant component in each of these categories . story_separator_special_tag replace_table_token_11_th 39 liquidity and capital resources cash flows the following table summarizes our cash flows for the years ended december 31 , 2018 , 2017 and 2016 : replace_table_token_12_th story_separator_special_tag million in proceeds from exercises of stock options . cash provided by financing activities was $ 9.2 million for the year ended december 31 , 2017 , consisting of $ 5.0 million in short-term debt obligations and $ 8.6 million in proceeds from the exercise of stock options , partially offset by $ 4.4 million for repurchases of common stock . cash provided by financing activities was $ 5.3 million for the year ended december 31 , 2016 , consisting of $ 5.7 million in proceeds from exercises of stock options , partially offset by $ 0.4 million for payments of acquisition-related contingent consideration . operating and capital expenditure requirements we believe , based on our current operating plan , that our cash balances and cash generated through operations and interest income will be sufficient to meet our anticipated cash requirements through at least the next 12 months . from time to time we may seek to sell equity or convertible debt securities or enter into credit facilities . the sale of equity and convertible debt securities may result in dilution to our shareholders . if we raise additional funds through the issuance of convertible debt securities or enter into credit facilities , these securities and debt holders could have rights senior to those of our common stock , and this debt could contain covenants that would restrict our operations . we may require additional capital beyond our currently forecasted amounts . any such required additional capital may not be available on terms acceptable to us , or at all . our future capital requirements will depend on many factors , including the following : the revenue growth in injection molding , cnc machining , 3d printing and sheet metal product lines ; costs of operations , including costs relating to expansion and growth ; the emergence of competing or complementary technological developments ; the costs of filing , prosecuting , defending and enforcing any patent claims and other intellectual product rights , or participating in litigation-related activities ; and the acquisition of businesses , products and technologies , although we currently have no commitments or agreements relating to any of these types of transactions . our recent annual capital expenditures have varied between 10 % and 20 % of annual revenue . we believe future growth capital expenditures , excluding any expenditures for buildings and maintenance capital we might purchase for our operations , are likely to vary between approximately 8 % and 12 % of annual revenue . 41 contractual obligations as of december 31 , 2018 , our contractual obligations and the effect such obligations are expected to have on our liquidity and cash flows in future periods were as follows : replace_table_token_13_th the table above reflects only payment obligations that are fixed and determinable . our commitments for operating leases relate to three of our united states manufacturing facilities ; our european sales , customer service and technical support offices ; manufacturing and office facilities located in germany ; and our japan facility . financing arrangements the following table summarizes our financing arrangements as of december 31 , 2018 and 2017 : december 31 , ( in thousands ) 2018 2017 revolving credit facility , with interest rates from 2.50 % to 2.59 % , due at maturity in november 2019 $ - $ 5,000 total financing obligations $ - $ 5,000 inflation we experience normal inflation and changing prices , primarily on our production materials and labor . we believe that inflation and changing prices have not had a material effect on our financial condition during the three most recent fiscal years . off-balance sheet arrangements since our inception , we have not engaged in any off-balance sheet arrangements , including the use of structured finance , special purpose entities or variable interest entities . critical accounting policies and use of estimates the discussion and analysis of our financial condition and results of operations is based upon our consolidated financial statements , which have been prepared in accordance with accounting principles generally accepted in the united states . the preparation of these financial statements requires us to make estimates , judgments and assumptions that affect the reported amount of assets , liabilities , revenue , expenses and related disclosures . on an ongoing basis , we evaluate our estimates , including those related to revenue recognition , goodwill , other intangible assets , stock-based compensation , and income taxes . we base our estimates of the carrying value of certain assets and liabilities on historical experience and on various other assumptions that we believe to be reasonable under the circumstances . in many cases , we could reasonably have used different accounting policies and estimates . in some cases , changes in the accounting estimates are reasonably likely to occur from period to period . management has discussed the development , selection and disclosure of these estimates with the audit committee of our board of directors . our actual results may differ significantly from these estimates under different assumptions or conditions . we believe the following critical accounting policies affect our more significant judgments used in the preparation of our consolidated financial statements . see the notes to consolidated financial statements included in item 8 . “ financial statements and supplementary data ” in this annual report on form 10-k for additional information about these critical accounting policies , as well as a description of our other accounting policies . 42 revenue recognition on january 1 , 2018 , we adopted asc 606 , revenue from contracts with customers , using the modified retrospective approach . we manufacture custom parts to specific customer orders that have no alternative use to us , and we believe there is a legally enforceable right to payment for performance

