Fair Value Measurements - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	$ 2,183,686	$ 1,760,100
U.S. Treasury securities and obligations of U.S. government agencies
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	27,661	16,741
Obligations of states, municipalities and political subdivisions [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	180,351	204,632
Corporate and other securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	1,051,412	832,892
Asset-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	565,912	353,006
Residential mortgage-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	297,602	293,962
Commercial mortgage-backed securities
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	60,748	58,867
Recurring
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	2,409,312	1,953,908
Recurring | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	197,591	162,416
Recurring | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	2,211,721	1,791,492
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]
Estimated Fair Value	2,183,686	1,760,100
Recurring | Fixed maturities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	27,661	16,741
Recurring | Fixed maturities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	2,156,025	1,743,359
Recurring | Fixed maturities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	27,661	16,741
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]
Estimated Fair Value	27,661	16,741
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]
Estimated Fair Value	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]
Estimated Fair Value	0	0
Recurring | Obligations of states, municipalities and political subdivisions [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	180,351	204,632
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]
Estimated Fair Value	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]
Estimated Fair Value	180,351	204,632
Recurring | Obligations of states, municipalities and political subdivisions [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Corporate and other securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	1,051,412	832,892
Recurring | Corporate and other securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Corporate and other securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	1,051,412	832,892
Recurring | Corporate and other securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Asset-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	565,912	353,006
Recurring | Asset-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Asset-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	565,912	353,006
Recurring | Asset-backed securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Residential mortgage-backed securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	297,602	293,962
Recurring | Residential mortgage-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Residential mortgage-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	297,602	293,962
Recurring | Residential mortgage-backed securities [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Commercial mortgage-backed securities
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	60,748	58,867
Recurring | Commercial mortgage-backed securities | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Commercial mortgage-backed securities | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	60,748	58,867
Recurring | Commercial mortgage-backed securities | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Estimated Fair Value	0	0
Recurring | Equity securities [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	196,848	152,471
Recurring | Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	165,266	114,309
Recurring | Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	31,582	38,162
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	110,125	104,202
Recurring | Exchange traded funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	110,125	104,202
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	31,582	38,162
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	31,582	38,162
Recurring | Nonredeemable preferred stock [Member] | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Common Stock [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	55,141	10,107
Recurring | Common Stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	55,141	10,107
Recurring | Common Stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	0	0
Recurring | Common 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	28,778	41,337
Recurring | Short-term Investments | Fair Value, Inputs, Level 1 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	4,664	31,366
Recurring | Short-term Investments | Fair Value, Inputs, Level 2 [Member]
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	24,114	9,971
Recurring | Short-term Investments | Level 3
Fair Value of Investments Measured on Recurring Basis [Line Items]
Fair value	$ 0	$ 0