Fair Value - Fair Value Measurements on a Recurring Basis by Asset Class and Level of Input (Details) | 12 Months Ended |
Dec. 31, 2018USD ($)fund | Dec. 31, 2017USD ($) | Dec. 31, 2016USD ($) |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | $ 748,523,000 | $ 745,961,000 | |
Equity securities | 11,853,000 | | |
Total available-for-sale securities | | 758,713,000 | |
Total | 763,582,000 | 763,529,000 | |
Other limited partnership investments: | | | |
Contributions made to the funds | 243,000 | 410,000 | $ 578,000 |
Distributions received from the funds | $ 3,387,000 | 10,768,000 | $ 16,113,000 |
Number of real estate funds reported under the fair value option | fund | 1 | | |
U.S. Treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | $ 208,412,000 | 11,734,000 | |
States and political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 159,023,000 | 259,264,000 | |
Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | | 503,000 | |
Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 249,947,000 | 346,523,000 | |
Residential mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 4,609,000 | 25,571,000 | |
Commercial mortgage-backed securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 46,515,000 | 32,804,000 | |
Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 64,239,000 | 58,034,000 | |
Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 15,778,000 | 11,528,000 | |
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 | | 11,659,000 | |
Nonredeemable preferred stock | Utilities Sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale equity securities | | 1,093,000 | |
Quoted prices in active markets for identical assets Level 1 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 0 | 0 | |
Equity securities | 1,809,000 | | |
Total available-for-sale securities | | 2,015,000 | |
Total | 1,809,000 | 2,015,000 | |
Observable inputs Level 2 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 735,946,000 | 735,882,000 | |
Equity securities | 10,044,000 | | |
Total available-for-sale securities | | 746,619,000 | |
Total | 745,990,000 | 746,619,000 | |
Unobservable inputs Level 3 | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 12,577,000 | 10,079,000 | |
Equity securities | 0 | | |
Total available-for-sale securities | | 10,079,000 | |
Total | 12,577,000 | 10,079,000 | |
Fair Value, Measurements, Recurring Basis | U.S. Treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 208,412,000 | 11,734,000 | |
Fair Value, Measurements, Recurring Basis | States and political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 159,023,000 | 259,264,000 | |
Fair Value, Measurements, Recurring Basis | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | | 503,000 | |
Fair Value, Measurements, Recurring Basis | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 249,947,000 | 346,523,000 | |
Fair Value, Measurements, 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 | 4,609,000 | 25,571,000 | |
Fair Value, Measurements, 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 | 46,515,000 | 32,804,000 | |
Fair Value, Measurements, Recurring Basis | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 64,239,000 | 58,034,000 | |
Fair Value, Measurements, Recurring Basis | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 15,778,000 | 11,528,000 | |
Fair Value, Measurements, Recurring Basis | Nonredeemable preferred stock | Financial Services Sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 11,853,000 | | |
Available-for-sale equity securities | | 11,659,000 | |
Fair Value, Measurements, 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 | | 1,093,000 | |
Fair Value, Measurements, Recurring Basis | Real estate | | | |
Other limited partnership investments: | | | |
Contributions made to the funds | 0 | 0 | |
Distributions received from the funds | 1,200,000 | 500,000 | |
Unfunded commitments | $ 0 | 0 | |
Number of real estate funds reported under the fair value option | fund | 1 | | |
Fair Value, Measurements, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets Level 1 | States and 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Quoted prices in active markets for identical assets Level 1 | Nonredeemable preferred stock | Financial Services Sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 1,809,000 | | |
Available-for-sale equity securities | | 2,015,000 | |
Fair Value, Measurements, Recurring Basis | Quoted prices in active markets for identical assets 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, Recurring Basis | Observable inputs Level 2 | U.S. Treasury | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 208,412,000 | 11,734,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | States and political subdivisions | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 159,023,000 | 259,264,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | Foreign government securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | | 503,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 237,370,000 | 338,644,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs 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 | 4,609,000 | 25,571,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs 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 | 46,515,000 | 32,804,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | Collateralized debt obligations | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 64,239,000 | 55,834,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | Other debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 15,778,000 | 11,528,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs Level 2 | Nonredeemable preferred stock | Financial Services Sector | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Equity securities | 10,044,000 | | |
Available-for-sale equity securities | | 9,644,000 | |
Fair Value, Measurements, Recurring Basis | Observable inputs 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 | | 1,093,000 | |
Fair Value, Measurements, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs Level 3 | States and 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, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs Level 3 | Corporate debt securities | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Available-for-sale debt securities | 12,577,000 | 7,879,000 | |
Fair Value, Measurements, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs 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 | 2,200,000 | |
Fair Value, Measurements, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs 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, Recurring Basis | Unobservable inputs 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, Recurring Basis | Fair value option using net asset value (NAV) | Real estate | | | |
Fair value measurements on a recurring basis by asset class and level of input | | | |
Other limited partnership investments | $ 3,206,000 | $ 4,816,000 | |