Investments | Investments The amortized cost, gross unrealized gains and losses and fair value of the investment portfolio at June 30, 2016 and December 31, 2015 are shown below. June 30, 2016 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses (1) Fair Value U.S. Treasury securities and obligations of U.S. government corporations and agencies $ 59,860 $ 2,276 $ (806 ) $ 61,330 Obligations of U.S. states and political subdivisions 1,968,194 109,789 (531 ) 2,077,452 Corporate debt securities 1,704,917 31,769 (6,721 ) 1,729,965 Asset-backed securities 104,221 236 (50 ) 104,407 Residential mortgage-backed securities 241,314 600 (3,574 ) 238,340 Commercial mortgage-backed securities 281,502 3,547 (891 ) 284,158 Collateralized loan obligations 61,355 44 (849 ) 60,550 Total debt securities 4,421,363 148,261 (13,422 ) 4,556,202 Equity securities 6,228 3,651 (3 ) 9,876 Total investment portfolio $ 4,427,591 $ 151,912 $ (13,425 ) $ 4,566,078 December 31, 2015 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses (1) Fair Value U.S. Treasury securities and obligations of U.S. government corporations and agencies $ 160,393 $ 2,133 $ (1,942 ) $ 160,584 Obligations of U.S. states and political subdivisions 1,766,407 33,410 (7,290 ) 1,792,527 Corporate debt securities 2,046,697 2,836 (44,770 ) 2,004,763 Asset-backed securities 116,764 56 (203 ) 116,617 Residential mortgage-backed securities 265,879 161 (8,392 ) 257,648 Commercial mortgage-backed securities 237,304 162 (3,975 ) 233,491 Collateralized loan obligations 61,345 3 (1,148 ) 60,200 Debt securities issued by foreign sovereign governments 29,359 2,474 (102 ) 31,731 Total debt securities 4,684,148 41,235 (67,822 ) 4,657,561 Equity securities 5,625 38 (18 ) 5,645 Total investment portfolio $ 4,689,773 $ 41,273 $ (67,840 ) $ 4,663,206 (1) At June 30, 2016 and December 31, 2015 , there were no other-than-temporary impairment losses recorded in other comprehensive income. During the first quarter of 2016, we substantially liquidated our Australian entities and repatriated most assets, including proceeds from the monetization of our Australian investment portfolio. As of June 30, 2016 we held no investments in foreign sovereign governments. As discussed in Note 3 - “Debt” we are required to maintain collateral of at least 102% of the outstanding principal balance of the Advance. As of June 30, 2016 we pledged eligible collateral with a total fair value of $166.6 million . The amortized cost and fair values of debt securities at June 30, 2016 , by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most asset-backed and mortgage-backed securities and collateralized loan obligations provide for periodic payments throughout their lives, they are listed below in separate categories. June 30, 2016 (In thousands) Amortized Cost Fair Value Due in one year or less $ 272,706 $ 273,365 Due after one year through five years 1,143,174 1,163,590 Due after five years through ten years 1,128,998 1,156,648 Due after ten years 1,188,093 1,275,144 $ 3,732,971 $ 3,868,747 Asset-backed securities 104,221 104,407 Residential mortgage-backed securities 241,314 238,340 Commercial mortgage-backed securities 281,502 284,158 Collateralized loan obligations 61,355 60,550 Total as of June 30, 2016 $ 4,421,363 $ 4,556,202 At June 30, 2016 and December 31, 2015 , the investment portfolio had gross unrealized losses of $13.4 million and $67.8 million , respectively. For those securities in an unrealized loss position, the length of time the securities were in such a position, as measured by their month-end fair values, is as follows: June 30, 2016 Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Treasury securities and obligations of U.S. government corporations and agencies $ 8,996 $ (806 ) $ — $ — $ 8,996 $ (806 ) Obligations of U.S. states and political subdivisions 30,347 (303 ) 15,842 (228 ) 46,189 (531 ) Corporate debt securities 110,610 (2,341 ) 167,209 (4,381 ) 277,819 (6,722 ) Asset-backed securities 13,440 (45 ) 8,047 (5 ) 21,487 (50 ) Residential mortgage-backed securities 2,383 (68 ) 203,939 (3,505 ) 206,322 (3,573 ) Commercial mortgage-backed securities 33,169 (553 ) 38,382 (338 ) 71,551 (891 ) Collateralized loan obligations — — 52,050 (849 ) 52,050 (849 ) Equity securities — — 154 (3 ) 154 (3 ) Total $ 198,945 $ (4,116 ) $ 485,623 $ (9,309 ) $ 684,568 $ (13,425 ) December 31, 2015 Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Treasury securities and obligations of U.S. government corporations and agencies $ 60,548 $ (1,467 ) $ 1,923 $ (475 ) $ 62,471 $ (1,942 ) Obligations of U.S. states and political subdivisions 417,615 (6,404 ) 37,014 (886 ) 454,629 (7,290 ) Corporate debt securities 1,470,628 (38,519 ) 114,982 (6,251 ) 1,585,610 (44,770 ) Asset-backed securities 86,604 (173 ) 5,546 (30 ) 92,150 (203 ) Residential mortgage-backed securities 35,064 (312 ) 209,882 (8,080 ) 244,946 (8,392 ) Commercial mortgage-backed securities 134,488 (2,361 ) 69,927 (1,614 ) 204,415 (3,975 ) Collateralized loan obligations — — 51,750 (1,148 ) 51,750 (1,148 ) Debt securities issued by foreign sovereign governments 4,463 (102 ) — — 4,463 (102 ) Equity securities 355 (8 ) 171 (10 ) 526 (18 ) Total $ 2,209,765 $ (49,346 ) $ 491,195 $ (18,494 ) $ 2,700,960 $ (67,840 ) The unrealized losses in all categories of our investments at June 30, 2016 and December 31, 2015 were primarily caused by the difference in interest rates at each respective period, compared to interest rates at the time of purchase. There were 211 and 303 securities in an unrealized loss position at June 30, 2016 and December 31, 2015 , respectively. During each of the three and six months ended June 30, 2016 and 2015 there were no other-than-temporary impairments (“OTTI”) recognized. The net realized investment gains on the investment portfolio are as follows: Three Months Ended Six Months Ended (In thousands) 2016 2015 2016 2015 Realized investment gains (losses) on investments: Fixed maturities $ 831 $ 161 $ 3,886 $ 26,485 Equity securities 5 5 6 8 Net realized investment gains $ 836 $ 166 $ 3,892 $ 26,493 Three Months Ended Six Months Ended (In thousands) 2016 2015 2016 2015 Realized investment gains (losses) on investments: Gains on sales $ 1,404 $ 785 $ 5,509 $ 27,991 Losses on sales (568 ) (619 ) (1,617 ) (1,498 ) Net realized investment gains $ 836 $ 166 $ 3,892 $ 26,493 |