Investments in debt and equity securities | Investments in debt and equity securities. The total fair values of the Company's investments in debt and equity securities are as follows: March 31, 2019 December 31, 2018 ($000 omitted) Investments in: Debt securities 590,115 602,020 Equity securities 37,533 33,997 627,648 636,017 As of March 31, 2019 and December 31, 2018 , the net unrealized investment gains relating to investments in equity securities held were $ 6.6 million and $ 2.9 million, respectively. The amortized costs and fair values of investments in debt securities are as follows: March 31, 2019 December 31, 2018 Amortized costs Fair values Amortized costs Fair values ($000 omitted) Municipal 60,467 61,348 61,779 61,934 Corporate 322,993 325,918 333,289 328,495 Foreign 195,177 196,430 200,667 198,938 U.S. Treasury Bonds 6,533 6,419 12,951 12,653 585,170 590,115 608,686 602,020 Foreign debt securities consist of Canadian government and corporate bonds, United Kingdom treasury and corporate bonds, and Mexican government bonds. Gross unrealized gains and losses on investments in debt securities are as follows: March 31, 2019 December 31, 2018 Gains Losses Gains Losses ($000 omitted) Municipal 945 64 482 327 Corporate 4,014 1,089 1,894 6,688 Foreign 2,336 1,083 1,402 3,131 U.S. Treasury Bonds 2 116 2 300 7,297 2,352 3,780 10,446 Debt securities as of March 31, 2019 mature, according to their contractual terms, as follows (actual maturities may differ due to call or prepayment rights): Amortized costs Fair values ($000 omitted) In one year or less 50,945 50,822 After one year through five years 326,286 328,615 After five years through ten years 176,344 178,348 After ten years 31,595 32,330 585,170 590,115 Gross unrealized losses on investments in debt securities and the fair values of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at March 31, 2019 , were: Less than 12 months More than 12 months Total Losses Fair values Losses Fair values Losses Fair values ($000 omitted) Municipal — — 64 9,099 64 9,099 Corporate 28 9,652 1,061 117,827 1,089 127,479 Foreign 36 16,905 1,047 88,177 1,083 105,082 U.S. Treasury Bonds — — 116 6,310 116 6,310 64 26,557 2,288 221,413 2,352 247,970 The number of specific debt investment holdings held in an unrealized loss position as of March 31, 2019 was 151 . Of these securities, 138 were in unrealized loss positions for more than 12 months. During 2019, the overall gross unrealized losses on debt securities decreased compared to the prior year-end, primarily due to the decrease in the overall interest rate environment which improved the market values of investments. Since the Company does not intend to sell and will more likely than not maintain each investment security until its maturity or anticipated recovery, and no significant credit risk is deemed to exist, these investments are not considered as other-than-temporarily impaired. The Company believes its investment portfolio is diversified and expects no material loss to result from the failure to perform by issuers of the debt securities it holds. Investments made by the Company are not collateralized. Gross unrealized losses on investments in debt securities and the fair values of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2018 , were: Less than 12 months More than 12 months Total Losses Fair values Losses Fair values Losses Fair values ($000 omitted) Municipal 91 13,366 236 11,645 327 25,011 Corporate 4,416 201,965 2,272 71,044 6,688 273,009 Foreign 158 11,424 2,973 137,793 3,131 149,217 U.S. Treasury Bonds — — 300 12,544 300 12,544 4,665 226,755 5,781 233,026 10,446 459,781 |