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Investments (Tables) | 6 Months Ended
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Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract] |
Schedule of Fair Values and Gross Unrealized Gains and Losses | Fair Values and Gross Unrealized Gains and Losses on Investments
| Amortized Cost |  | Gross Unrealized |  | Fair Value
|  | Gains |  | Losses |
As of June 30, 2019 | (In Thousands)
U.S. Treasury securities and obligations of U.S. government agencies | $ | 48,193 |  |  | $ | 688 |  |  | $ | (116 | ) |  | $ | 48,765 |
Municipal debt securities | 91,650 |  |  | 1,497 |  |  | (73 | ) |  | 93,074 |
Corporate debt securities | 634,188 |  |  | 18,569 |  |  | (785 | ) |  | 651,972 |
Asset-backed securities | 168,251 |  |  | 3,216 |  |  | (36 | ) |  | 171,431 |
Total bonds | 942,282 |  |  | 23,970 |  |  | (1,010 | ) |  | 965,242 |
Short-term investments | 52,261 |  |  | 104 |  |  | — |  |  | 52,365 |
Total investments | $ | 994,543 |  |  | $ | 24,074 |  |  | $ | (1,010 | ) |  | $ | 1,017,607 |
| Amortized Cost |  | Gross Unrealized |  | Fair Value
|  | Gains |  | Losses |
As of December 31, 2018 | (In Thousands)
U.S. Treasury securities and obligations of U.S. government agencies | $ | 48,171 |  |  | $ | 35 |  |  | $ | (1,376 | ) |  | $ | 46,830 |
Municipal debt securities | 92,014 |  |  | 206 |  |  | (963 | ) |  | 91,257 |
Corporate debt securities | 554,079 |  |  | 847 |  |  | (11,688 | ) |  | 543,238 |
Asset-backed securities | 171,990 |  |  | 792 |  |  | (1,457 | ) |  | 171,325 |
Total bonds | 866,254 |  |  | 1,880 |  |  | (15,484 | ) |  | 852,650 |
Short-term investments | 58,733 |  |  | 107 |  |  | — |  |  | 58,840 |
Total investments | $ | 924,987 |  |  | $ | 1,987 |  |  | $ | (15,484 | ) |  | $ | 911,490 |
Schedule of Investments by Industry Group | The following table presents a breakdown of the fair value of our corporate debt securities by issuer industry group as of June 30, 2019 and December 31, 2018:
| June 30, 2019 |  | December 31, 2018
Financial | 38 | % |  | 38 | %
Consumer | 27 |  |  | 27 |
Communications | 10 |  |  | 12 |
Utilities | 9 |  |  | 7 |
Industrial | 8 |  |  | 7 |
Technology | 6 |  |  | 6 |
Energy | 1 |  |  | 2 |
Other | 1 |  |  | 1 |
Total | 100 | % |  | 100 | %
Schedule of Investments by Maturity | The amortized cost and fair values of available-for-sale securities as of June 30, 2019 and December 31, 2018, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most asset-backed securities provide for periodic payments throughout their lives, they are listed below in a separate category.
As of June 30, 2019 | Amortized Cost |  | Fair Value
| (In Thousands)
Due in one year or less | $ | 99,314 |  |  | $ | 99,375 |
Due after one through five years | 412,820 |  |  | 420,131 |
Due after five through ten years | 300,990 |  |  | 312,792 |
Due after ten years | 13,168 |  |  | 13,878 |
Asset-backed securities | 168,251 |  |  | 171,431 |
Total investments | $ | 994,543 |  |  | $ | 1,017,607 |
As of December 31, 2018 | Amortized Cost |  | Fair Value
| (In Thousands)
Due in one year or less | $ | 76,087 |  |  | $ | 76,104 |
Due after one through five years | 352,282 |  |  | 347,701 |
Due after five through ten years | 318,728 |  |  | 310,633 |
Due after ten years | 5,900 |  |  | 5,727 |
Asset-backed securities | 171,990 |  |  | 171,325 |
Total investments | $ | 924,987 |  |  | $ | 911,490 |
Schedule of Aging Unrealized Losses | or those securities in an unrealized loss position, the length of time the securities were in such a position is as follows:
| Less Than 12 Months |  | 12 Months or Greater |  | Total
| # of Securities | Fair Value | Unrealized Losses |  | # of Securities | Fair Value | Unrealized Losses |  | # of Securities | Fair Value | Unrealized Losses
As of June 30, 2019 |  | (Dollars in Thousands)
U.S. Treasury securities and obligations of U.S. government agencies | — |  | $ | — |  | $ | — |  |  | 5 |  | $ | 13,750 |  | $ | (116 | ) |  | 5 |  | $ | 13,750 |  | $ | (116 | )
Municipal debt securities(1) | 1 |  | 2,000 |  | — |  |  | 10 |  | 15,025 |  | (73 | ) |  | 11 |  | 17,025 |  | (73 | )
Corporate debt securities | 13 |  | 24,737 |  | (199 | ) |  | 33 |  | 51,099 |  | (586 | ) |  | 46 |  | 75,836 |  | (785 | )
Asset-backed securities | 2 |  | 8,786 |  | (33 | ) |  | 6 |  | 1,953 |  | (3 | ) |  | 8 |  | 10,739 |  | (36 | )
Total | 16 |  | $ | 35,523 |  | $ | (232 | ) |  | 54 |  | $ | 81,827 |  | $ | (778 | ) |  | 70 |  | $ | 117,350 |  | $ | (1,010 | )
(1) | Includes securities with unrealized losses of less than 12 months which are not identifiable in the schedule due to rounding.
| Less Than 12 Months |  | 12 Months or Greater |  | Total
| # of Securities | Fair Value | Unrealized Losses |  | # of Securities | Fair Value | Unrealized Losses |  | # of Securities | Fair Value | Unrealized Losses
As of December 31, 2018 |  | (Dollars in Thousands)
U.S. Treasury securities and obligations of U.S. government agencies | — |  | $ | — |  | $ | — |  |  | 19 |  | $ | 41,817 |  | $ | (1,376 | ) |  | 19 |  | $ | 41,817 |  | $ | (1,376 | )
Municipal debt securities | 4 |  | 7,409 |  | (11 | ) |  | 31 |  | 58,658 |  | (952 | ) |  | 35 |  | 66,067 |  | (963 | )
Corporate debt securities | 118 |  | 226,477 |  | (3,952 | ) |  | 126 |  | 221,675 |  | (7,736 | ) |  | 244 |  | 448,152 |  | (11,688 | )
Asset-backed securities | 25 |  | 36,017 |  | (1,136 | ) |  | 22 |  | 33,988 |  | (321 | ) |  | 47 |  | 70,005 |  | (1,457 | )
Total | 147 |  | $ | 269,903 |  | $ | (5,099 | ) |  | 198 |  | $ | 356,138 |  | $ | (10,385 | ) |  | 345 |  | $ | 626,041 |  | $ | (15,484 | )
Schedule of Components of Net Investment Income | The following table presents the components of net investment income:
| For the three months ended June 30, |  | For the six months ended June 30,
| 2019 |  | 2018 |  | 2019 |  | 2018
| (In Thousands)
Investment income | $ | 7,741 |  |  | $ | 5,937 |  |  | $ | 15,237 |  |  | $ | 10,719 |
Investment expenses | (112 | ) |  | (202 | ) |  | (225 | ) |  | (410 | )
Net investment income | $ | 7,629 |  |  | $ | 5,735 |  |  | $ | 15,012 |  |  | $ | 10,309 |
Schedule of Net Realized Investment Gains (Losses) | The following table presents the components of net realized investment losses:
| For the three months ended June 30, |  | For the six months ended June 30,
| 2019 |  | 2018 |  | 2019 |  | 2018
| (In Thousands)
Gross realized investment gains | $ | 22 |  |  | $ | 59 |  |  | $ | 217 |  |  | $ | 59 |
Gross realized investment losses | (135 | ) |  | — |  |  | (517 | ) |  | — |
Net realized investment losses | $ | (113 | ) |  | $ | 59 |  |  | $ | (300 | ) |  | $ | 59 |

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