15. SEGMENT REPORTING The U.S. Reinsurance operation writes property and casualty reinsurance and specialty lines of business, including Marine, Aviation, Surety and Accident and Health ("A&amp;H") business, on both a treaty and facultative basis, through reinsurance brokers, as well as directly with ceding companies primarily within the U.S. The International operation writes non-U.S. property and casualty reinsurance through Everest Re's branches in Canada and Singapore and through offices in Brazil, Miami and New Jersey. The Bermuda operation provides reinsurance and insurance to worldwide property and casualty markets through brokers and directly with ceding companies from its Bermuda office and reinsurance to the United Kingdom and European markets through its UK branch and Ireland Re. The Insurance operation writes property and casualty insurance directly and through brokers, surplus lines brokers and general agents within the U.S., Canada and Europe. These segments are managed independently, but conform with corporate guidelines with respect to pricing, risk management, control of aggregate catastrophe exposures, capital, investments and support operations. Management generally monitors and evaluates the financial performance of these operating segments based upon their underwriting results. Underwriting results include earned premium less losses and loss adjustment expenses ("LAE") incurred, commission and brokerage expenses and other underwriting expenses. We measure our underwriting results using ratios, in particular loss, commission and brokerage and other underwriting expense ratios, which, respectively, divide incurred losses, commissions and brokerage and other underwriting expenses by premiums earned. For inter-affiliate reinsurance and business written through the Lloyd's Syndicate, business is generally reported within the segment in which the business was first produced, consistent with how the business is managed. The Company does not maintain separate balance sheet data for its operating segments. Accordingly, the Company does not review and evaluate the financial results of its operating segments based upon balance sheet data. The following tables present the underwriting results for the operating segments for the periods indicated: Three Months Ended U.S. Reinsurance March 31, (Dollars in thousands) 2019 2018 Gross written premiums $ 764,146 $ 644,222 Net written premiums 669,707 545,831 Premiums earned $ 626,471 $ 563,385 Incurred losses and LAE 320,104 545,193 Commission and brokerage 167,102 127,320 Other underwriting expenses 15,591 16,886 Underwriting gain (loss) $ 123,674 $ (126,014 ) Three Months Ended International March 31, (Dollars in thousands) 2019 2018 Gross written premiums $ 400,054 $ 366,724 Net written premiums 375,505 345,155 Premiums earned $ 350,935 $ 343,604 Incurred losses and LAE 254,135 127,024 Commission and brokerage 81,425 82,177 Other underwriting expenses 8,681 10,576 Underwriting gain (loss) $ 6,694 $ 123,827 Three Months Ended Bermuda March 31, (Dollars in thousands) 2019 2018 Gross written premiums $ 367,851 $ 415,686 Net written premiums 349,341 394,968 Premiums earned $ 330,113 $ 319,134 Incurred losses and LAE 197,959 129,513 Commission and brokerage 74,110 81,487 Other underwriting expenses 11,497 10,133 Underwriting gain (loss) $ 46,547 $ 98,001 Three Months Ended Insurance March 31, (Dollars in thousands) 2019 2018 Gross written premiums $ 595,057 $ 504,975 Net written premiums 457,145 386,252 Premiums earned $ 425,178 $ 393,304 Incurred losses and LAE 276,352 255,447 Commission and brokerage 66,837 66,655 Other underwriting expenses 63,216 58,689 Underwriting gain (loss) $ 18,773 $ 12,513 The following table reconciles the underwriting results for the operating segments to income before taxes as reported in the consolidated statements of operations and comprehensive income (loss) for the periods indicated: Three Months Ended March 31, (Dollars in thousands) 2019 2018 Underwriting gain (loss) $ 195,688 $ 108,327 Net investment income 140,976 138,294 Net realized capital gains (losses) 92,232 (24,901 ) Net derivative gain (loss) 3,231 273 Corporate expenses (6,652 ) (8,996 ) Interest, fee and bond issue cost amortization expense (7,631 ) (7,418 ) Other income (expense) (9,053 ) 12,064 Income (loss) before taxes $ 408,791 $ 217,643 The Company produces business in the U.S., Bermuda and internationally. The net income deriving from and assets residing in the individual foreign countries in which the Company writes business are not identifiable in the Company's financial records. Based on gross written premium, the table below presents the largest country, other than the U.S., in which the Company writes business, for the periods indicated: Three Months Ended March 31, (Dollars in thousands) 2019 2018 United Kingdom gross written premium $ 263,857 $ 258,259 No other country represented more than 5% of the Company's revenues.