Fair Value Measurements - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	$ 1,461,415	$ 1,392,066
U.S. Treasury securities and obligations of U.S. government agencies
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	13,984	6,847
Obligations of states, municipalities and political subdivisions [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	217,759	228,045
Corporate and other securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	529,086	458,487
Asset-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	273,658	301,775
Residential mortgage-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	358,035	337,685
Commercial mortgage-backed securities
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	68,893	59,227
Recurring
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	1,625,814	1,564,677
Recurring | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	133,272	130,236
Recurring | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	1,492,542	1,434,441
Recurring | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Fixed maturities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	1,461,415	1,392,066
Recurring | Fixed maturities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	13,984	6,847
Recurring | Fixed maturities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	1,447,431	1,385,219
Recurring | Fixed maturities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	13,984	6,847
Recurring | U.S. Treasury securities and obligations of U.S. government agencies | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	13,984	6,847
Recurring | U.S. Treasury securities and obligations of U.S. government agencies | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | U.S. Treasury securities and obligations of U.S. government agencies | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Obligations of states, municipalities and political subdivisions [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	217,759	228,045
Recurring | Obligations of states, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Obligations of states, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	217,759	228,045
Recurring | Obligations of states, municipalities and political subdivisions [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Corporate and other securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	529,086	458,487
Recurring | Corporate and other securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Corporate and other securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	529,086	458,487
Recurring | Corporate and other securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Asset-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	273,658	301,775
Recurring | Asset-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Asset-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	273,658	301,775
Recurring | Asset-backed securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Residential mortgage-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	358,035	337,685
Recurring | Residential mortgage-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Residential mortgage-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	358,035	337,685
Recurring | Residential mortgage-backed securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Commercial mortgage-backed securities
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	68,893	59,227
Recurring | Commercial mortgage-backed securities | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Commercial mortgage-backed securities | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	68,893	59,227
Recurring | Commercial mortgage-backed securities | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fixed-maturity securities, available for sale, at fair value (amortized cost: $1,521,792 – 2022; $1,371,519 – 2021)	0	0
Recurring | Equity securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	163,574	172,611
Recurring | Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	119,288	123,389
Recurring | Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	44,286	49,222
Recurring | Equity securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Exchange traded funds [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	119,288	123,389
Recurring | Exchange traded funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	119,288	123,389
Recurring | Exchange traded funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Exchange traded funds [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Nonredeemable preferred stock [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	44,286	49,222
Recurring | Nonredeemable preferred stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Nonredeemable preferred stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	44,286	49,222
Recurring | Nonredeemable preferred stock [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	$ 0
Recurring | Short-term Investments
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	825
Recurring | Short-term Investments | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0
Recurring | Short-term Investments | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	825
Recurring | Short-term Investments | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	$ 0