Fair Value (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended |
Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017 |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | $ 704,195 | | |
Equity securities | 12,511 | | |
Total available-for-sale securities | 704,195 | | $ 758,713 |
Other limited partnership investments: | | | |
Contributions made to the funds | 217 | $ 330 | |
Distributions received from the funds | 3,046 | $ 7,986 | |
Fixed maturities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | | | 745,961 |
U.S. treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 36,425 | | 11,734 |
States & political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 256,865 | | 259,264 |
Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | | | 503 |
Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 277,669 | | 346,523 |
Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 2,494 | | 25,571 |
Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 46,860 | | 32,804 |
Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 65,294 | | 58,034 |
Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 18,588 | | 11,528 |
Nonredeemable preferred stock | Financial services sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | | 11,659 |
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 non-recurring basis | | | |
Fair value measurements on a non-recurring basis | | | |
Assets measured at fair value on a non-recurring basis | 0 | | |
Fair value measurements on a non-recurring basis | | | |
Liabilities measured at fair value on a non-recurring basis | 0 | | |
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 | 720,023 | | 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 | 704,195 | | 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 | 36,425 | | 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 | 256,865 | | 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 | | | 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 | 277,669 | | 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 | 2,494 | | 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 | 46,860 | | 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 | 65,294 | | 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 | 18,588 | | 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 | 12,511 | | |
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 | 12,511 | | |
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 | | | |
Other limited partnership investments: | | | |
Contributions made to the funds | 0 | | 0 |
Distributions received from the funds | 1,200 | | 500 |
Unfunded commitments | $ 0 | | $ 0 |
Fair value measurements on a recurring basis | Real estate | Minimum | | | |
Other limited partnership 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 limited partnership 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 | $ 1,981 | | 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 |
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 | 1,981 | | |
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 | 1,981 | | |
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 | 705,550 | | 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 | 695,020 | | 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 | 36,425 | | 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 | 256,865 | | 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 | | | 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 | 269,399 | | 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 | 2,494 | | 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 | 46,860 | | 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 | 65,294 | | 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 | 17,683 | | 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 | 10,530 | | |
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 | 10,530 | | |
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 | 9,175 | | 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 | 9,175 | | 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 |
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 | 8,270 | | 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 | 905 | | 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 |
Fair value measurements on a recurring basis | Net Asset Value (NAV) | Real estate | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Other limited partnership investments | $ 3,317 | | $ 4,816 |