Note 13Reportable Segments We segregate our business into five reportable segments: the Power segment, the Pipeline segment, the Utilities segment, the Transmission segment, which is a new reportable segment created in connection with the acquisition of Willbros, and the Civil segment. Each of our reportable segments is comprised of similar business units that specialize in services unique to the segment. Driving the end-user focused segments are differences in the economic characteristics of each segment, the nature of the services provided by each segment; the production processes of each segment; the type or class of customer using the segments services; the methods used by the segment to provide the services; and the regulatory environment of each segments customers. The classification of revenue and gross profit for segment reporting purposes can at times require judgment on the part of management. Our segments may perform services across industries or perform joint services for customers in multiple industries. To determine reportable segment gross profit, certain allocations, including allocations of shared and indirect costs, such as facility costs, equipment costs and indirect operating expenses, were made. The following is a brief description of the reportable segments: The Power segment operates throughout the United States and in Canada and specializes in a range of services that include full EPC project delivery, turnkey construction, retrofits, upgrades, repairs, outages, and maintenance for entities in the petroleum, petrochemical, water, and other industries. The Pipeline segment operates throughout the United States and specializes in a range of services, including pipeline construction, pipeline maintenance, pipeline facility work, compressor stations, pump stations, metering facilities, and other pipeline related services for entities in the petroleum and petrochemical industries. The Utilities segment operates primarily in California, the Midwest, and the Southeast regions of the United States and specializes in a range of services, including utility line installation and maintenance, gas and electric distribution, streetlight construction, substation work, and fiber optic cable installation. The Transmission segment operates primarily in the Southeastern and Gulf Coast regions of the United States and specializes in a range of services in electric and gas transmission and distribution, including comprehensive engineering, procurement, maintenance and construction, repair, and restoration of utility infrastructure. The Civil segment operates primarily in the Southeastern and Gulf Coast regions of the United States and specializes in highway and bridge construction, airport runway and taxiway construction, demolition, heavy earthwork, soil stabilization, mass excavation, and drainage projects. All intersegment revenue and gross profit, which was immaterial, has been eliminated in the following tables. Segment Revenue Revenue by segment for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands): 2018 2017 2016 % of % of % of Total Total Total Segment Revenue Revenue Revenue Revenue Revenue Revenue Power $ 694,048 23.6% $ 606,125 25.5% $ 478,653 24.0% Pipeline 590,937 20.1% 465,570 19.5% 401,931 20.1% Utilities 902,772 30.7% 806,523 33.9% 637,212 31.9% Transmission (1) 286,749 9.8%     Civil 464,972 15.8% 501,777 21.1% 479,152 24.0% Total $ 2,939,478 100.0% $ 2,379,995 100.0% $ 1,996,948 100.0% (1) Represents results from the June 1, 2018 acquisition date of Willbros to December 31, 2018 . Segment Gross Profit Gross profit by segment for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands): 2018 2017 2016 % of % of % of Segment Segment Segment Gross Profit Revenue Gross Profit Revenue Gross Profit Revenue Power $ 109,789 15.8% $ 65,675 10.8% $ 49,807 10.4% Pipeline 66,602 11.3% 92,087 19.8% 68,100 16.9% Utilities 111,825 12.4% 113,037 14.0% 100,071 15.7% Transmission (1) 31,904 11.1%     Civil 5,617 1.2% 7,635 1.5% (16,671) (3.5%) Total $ 325,737 11.1% $ 278,434 11.7% $ 201,307 10.1% (1) Represents results from the June 1, 2018 acquisition date of Willbros to December 31, 2018 . Geographic Region  Revenue and Total Assets The majority of our revenue is derived from customers in the United States with approximately 2.9%, 0.3% and 0.6% generated from sources outside of the United States for the years ended December 31, 2018, 2017, and 2016, respectively. At December 31, 2018 and 2017, approximately 2.8% and 1.0%, respectively of total assets were located outside of the United States.