Segment Information ? The Company has four reportable segments, three of which are separately managed business units and the fourth (Corporate and Other) includes the Companys remaining operations. The Excess and Surplus Lines segment primarily offers commercial excess and surplus lines liability and excess property insurance products. The Specialty Admitted Insurance segment offers workers compensation insurance coverage as well as specialty admitted fronting and program business. The Casualty Reinsurance segment offers commercial liability and non-catastrophe property reinsurance to U.S. insurance companies and to the Companys U.S.-based insurance subsidiaries. The Corporate and Other segment consists of certain management and treasury activities of James River Group, James River UK, and JRG Holdings as well as interest expense associated with senior debt and Junior Subordinated Debt, and investment income from investments classified as trading or other invested assets. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Segment revenues for each reportable segment consist of net earned premiums, net investment income, and realized and unrealized (losses) gains on investments. Segment profit (loss) for each reportable segment is measured by underwriting profit (loss), which is generally defined as net earned premiums less losses and loss adjustment expenses and other operating expenses of the operating segments. Gross fee income of the Excess and Surplus Lines segment are included in that segments underwriting profit (loss). Gross fee income of $13.9 million , $17.0 million and $10.1 million was included in underwriting profit for the years ended December 31, 2018 , 2017 and 2016 , respectively. Segment results are reported prior to the effects of the intercompany reinsurance agreements between the Companys insurance subsidiaries. All gross written premiums and net earned premiums for all periods presented were generated from policies issued to U.S. based insureds. ? Excess and Surplus Lines Specialty Admitted Insurance Casualty Reinsurance Corporate and Other Total ? (in thousands) As of and for the Year Ended December 31, 2018 ? ? ? ? ? ? Gross written premiums $ 656,538 $ 374,346 $ 135,889 $  ? $ 1,166,773 Net earned premiums 555,684 55,146 204,568  ? 815,398 Segment revenues 580,785 56,717 243,178 4,919 ? 885,599 Net investment income 14,456 3,262 38,838 4,700 ? 61,256 Interest expense    11,553 ? 11,553 Underwriting profit of operating segments 42,834 6,972 5,103  ? 54,909 Segment goodwill 181,831    ? 181,831 Segment assets 972,111 633,689 1,453,754 77,222 ? 3,136,776 ? Excess and Surplus Lines Specialty Admitted Insurance Casualty Reinsurance Corporate and Other Total ? (in thousands) As of and for the Year Ended December 31, 2017 ? ? ? ? ? Gross written premiums $ 530,120 $ 316,430 $ 235,355 $  $ 1,081,905 Net earned premiums 463,521 68,110 209,478  741,109 Segment revenues 493,853 70,366 240,751 12,655 817,625 Net investment income 15,014 2,532 31,507 12,066 61,119 Interest expense    8,974 8,974 Underwriting profit (loss) of operating segments 29,693 3,166 (1,765 )  31,094 Segment goodwill 181,831    181,831 Segment assets 843,486 439,416 1,379,866 93,927 2,756,695 As of and for the Year Ended December 31, 2016 ? ? ? ? ? Gross written premiums $ 370,844 $ 182,221 $ 184,333 $  $ 737,398 Net earned premiums 301,404 52,281 161,978  515,663 Segment revenues 331,090 55,412 190,064 9,661 586,227 Net investment income 18,051 2,542 27,257 4,788 52,638 Interest expense    8,448 8,448 Underwriting profit (loss) of operating segments 47,235 2,872 (194 )  49,913 Segment goodwill 181,831    181,831 Segment assets 740,144 300,519 1,195,230 110,640 2,346,533 The following table reconciles the underwriting profit (loss) of insurance segments by individual segment to income before taxes: ? Year Ended December 31, ? 2018 2017 2016 ? (in thousands) Underwriting profit (loss) of the operating segments: ? ? ? ? ? Excess and Surplus Lines $ 42,834 $ 29,693 $ 47,235 Specialty Admitted Insurance 6,972 3,166 2,872 Casualty Reinsurance 5,103 (1,765 ) (194 ) Total underwriting profit of operating segments 54,909 31,094 49,913 Other operating expenses of the Corporate and Other segment (26,903 ) (25,330 ) (20,433 ) Underwriting profit 28,006 5,764 29,480 Net investment income 61,256 61,119 52,638 Net realized and unrealized (losses) gains on investments (5,479 ) (1,989 ) 7,565 Other income 505 361 295 Other expenses (1,300 ) (539 ) (1,590 ) Interest expense (11,553 ) (8,974 ) (8,448 ) Amortization of intangible assets (597 ) (597 ) (597 ) Income before income taxes $ 70,838 $ 55,145 $ 79,343 The Company currently has 15 underwriting divisions, including 13 in the Excess and Surplus Lines segment, one in the Specialty Admitted Insurance segment, and one in the Casualty Reinsurance segment. Each underwriting division focuses on a specific industry group or coverage. Gross written premiums by segment and underwriting division are presented below: ? Year Ended December 31, ? 2018 2017 2016 ? (in thousands) Commercial Auto $ 322,126 ? $ 247,960 ? $ 110,050 Manufacturers and Contractors 79,160 ? 85,719 ? 83,279 Excess Casualty 66,452 ? 51,160 ? 43,574 General Casualty 54,127 ? 38,097 ? 36,858 Energy 33,942 ? 29,704 ? 29,709 Allied Health 30,450 ? 19,181 ? 14,413 Excess Property 16,963 ? 14,447 ? 14,083 Life Sciences 16,636 ? 12,981 ? 11,132 Small Business 14,808 ? 11,307 ? 9,104 Professional Liability 5,916 ? 6,326 ? 8,361 Environmental 10,499 ? 7,920 ? 5,321 Medical Professionals 1,774 ? 2,297 ? 2,739 Sports and Entertainment 3,685 ? 3,021 ? 2,221 Total Excess and Surplus Lines segment 656,538 ? 530,120 ? 370,844 Specialty Admitted Insurance segment 374,346 ? 316,430 ? 182,221 Casualty Reinsurance segment 135,889 ? 235,355 ? 184,333 Total $ 1,166,773 ? $ 1,081,905 ? $ 737,398 The Company does business with two brokers that generated $358.3 million and $81.4 million of gross written premiums for the Excess and Surplus Lines segment for the year ended December 31, 2018 , representing 30.7% (BB&amp;T Insurance Services) and 7.0% of consolidated gross written premiums and 54.6% and 12.4% of the Excess and Surplus Lines segments gross written premiums, respectively. The Company has agency contracts with various branches within the aforementioned brokers. No other broker generated 10.0% or more of the gross written premiums for the Excess and Surplus Lines segment for the year ended December 31, 2018 . The Company does business with one insured (Rasier LLC) that generated $294.3 million of gross written premiums and $13.9 million of gross fee income for the Excess and Surplus Lines segment for the year ended December 31, 2018 , representing 25.2% of consolidated gross written premiums and 44.8% of the Excess and Surplus Lines segments gross written premiums. No other insured generated 10.0% or more of the gross written premiums for the Excess and Surplus Lines segment. The Specialty Admitted Insurance segment accepts applications for insurance from a variety of sources, including independent retail agents, program administrators and managing general agents (MGAs). The Company does business with one agency (Atlas General Insurance Services) that generated $201.7 million of gross written premiums for the Specialty Admitted Insurance segment for the year ended December 31, 2018 , representing 17.3% of the consolidated gross written premiums and 53.9% of the Specialty Admitted Insurance segments gross written premiums. No other agency generated 10.0% or more of the gross written premiums for the Specialty Admitted Insurance segment for the year ended December 31, 2018 . The Company does business with two brokers that generated $54.0 million and $42.3 million of gross written premiums for the Casualty Reinsurance segment for the year ended December 31, 2018 , representing 4.6% and 3.6% of consolidated gross written premiums and 39.8% and 31.1% of the Casualty Reinsurance segments gross written premiums, respectively. No other broker generated 10.0% or more of the gross written premiums for the Casualty Reinsurance segment for the year ended December 31, 2018 . The Casualty Reinsurance segment assumed business from three unaffiliated ceding companies that generated $83.4 million , $22.1 million , and $20.8 million of gross written premiums for the year ended December 31, 2018 , representing 7.1% , 1.9% , and 1.8% of consolidated gross written premiums and 61.4% , 16.2% , and 15.3% of the Casualty Reinsurance segments gross written premiums, respectively.