Fair Value (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | $ 729,804 | | |
Equity securities | 12,583 | | |
Total available-for-sale securities | 729,804 | | $ 758,713 |
Other investments: | | | |
Contributions made to the funds | 31 | $ 111 | |
Distributions received from the funds | 910 | $ 3,396 | |
Fair value measurements on a recurring basis | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Total available-for-sale securities | | | 758,713 |
Total | 746,816 | | 763,529 |
Fair value measurements on a recurring basis | Fixed maturities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 729,804 | | 745,961 |
Fair value measurements on a recurring basis | U.S. treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 36,464 | | 11,734 |
Fair value measurements on a recurring basis | States & political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 261,152 | | 259,264 |
Fair value measurements on a recurring basis | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 501 | | 503 |
Fair value measurements on a recurring basis | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 299,599 | | 346,523 |
Fair value measurements on a recurring basis | Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 24,110 | | 25,571 |
Fair value measurements on a recurring basis | Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 33,675 | | 32,804 |
Fair value measurements on a recurring basis | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 71,305 | | 58,034 |
Fair value measurements on a recurring basis | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 2,998 | | 11,528 |
Fair value measurements on a recurring basis | Equity securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 12,583 | | |
Fair value measurements on a recurring basis | Nonredeemable preferred stock | Financial services sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 12,583 | | |
Available-for-sale equity securities | | | 11,659 |
Fair value measurements on a recurring basis | Nonredeemable preferred stock | Utilities sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | | 1,093 |
Fair value measurements on a recurring basis | Real estate | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Other investments | 4,429 | | 4,816 |
Other investments: | | | |
Contributions made to the funds | 0 | | 0 |
Distributions received from the funds | 0 | | 500 |
Unfunded commitments | $ 0 | | $ 0 |
Fair value measurements on a recurring basis | Real estate | Minimum | | | |
Other investments: | | | |
Underlying assets, liquidation period from inception of fund (in years) | 5 years | | 5 years |
Fair value measurements on a recurring basis | Real estate | Maximum | | | |
Other investments: | | | |
Underlying assets, liquidation period from inception of fund (in years) | 10 years | | 10 years |
Fair value measurements on a recurring basis | Level 1 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Total available-for-sale securities | | | $ 2,015 |
Total | $ 1,993 | | 2,015 |
Fair value measurements on a recurring basis | Level 1 | Fixed maturities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | U.S. treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | States & political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 1 | Equity securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 1,993 | | |
Fair value measurements on a recurring basis | Level 1 | Nonredeemable preferred stock | Financial services sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 1,993 | | |
Available-for-sale equity securities | | | 2,015 |
Fair value measurements on a recurring basis | Level 1 | Nonredeemable preferred stock | Utilities sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | | 0 |
Fair value measurements on a recurring basis | Level 2 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Total available-for-sale securities | | | 746,619 |
Total | 734,085 | | 746,619 |
Fair value measurements on a recurring basis | Level 2 | Fixed maturities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 723,495 | | 735,882 |
Fair value measurements on a recurring basis | Level 2 | U.S. treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 36,464 | | 11,734 |
Fair value measurements on a recurring basis | Level 2 | States & political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 261,152 | | 259,264 |
Fair value measurements on a recurring basis | Level 2 | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 501 | | 503 |
Fair value measurements on a recurring basis | Level 2 | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 293,290 | | 338,644 |
Fair value measurements on a recurring basis | Level 2 | Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 24,110 | | 25,571 |
Fair value measurements on a recurring basis | Level 2 | Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 33,675 | | 32,804 |
Fair value measurements on a recurring basis | Level 2 | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 71,305 | | 55,834 |
Fair value measurements on a recurring basis | Level 2 | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 2,998 | | 11,528 |
Fair value measurements on a recurring basis | Level 2 | Equity securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 10,590 | | |
Fair value measurements on a recurring basis | Level 2 | Nonredeemable preferred stock | Financial services sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 10,590 | | |
Available-for-sale equity securities | | | 9,644 |
Fair value measurements on a recurring basis | Level 2 | Nonredeemable preferred stock | Utilities sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | | 1,093 |
Fair value measurements on a recurring basis | Level 3 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Total available-for-sale securities | | | 10,079 |
Total | 6,309 | | 10,079 |
Fair value measurements on a recurring basis | Level 3 | Fixed maturities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 6,309 | | 10,079 |
Fair value measurements on a recurring basis | Level 3 | U.S. treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | States & political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 6,309 | | 7,879 |
Fair value measurements on a recurring basis | Level 3 | Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 2,200 |
Fair value measurements on a recurring basis | Level 3 | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | | 0 |
Fair value measurements on a recurring basis | Level 3 | Equity securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 0 | | |
Fair value measurements on a recurring basis | Level 3 | Nonredeemable preferred stock | Financial services sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | $ 0 | | |
Available-for-sale equity securities | | | 0 |
Fair value measurements on a recurring basis | Level 3 | Nonredeemable preferred stock | Utilities sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | | $ 0 |