Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets:
Fixed maturities available for sale, at fair value	$ 3,472,472	$ 3,833,722
Fixed maturities, trading	43,434	43,670
Equity investments	143,738	214,807
U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	221,608	238,507
U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	19,934	20,234
State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	439,450	519,196
Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	389,540	453,941
Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	9,704	14,141
Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	194,090	231,483
Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	416,694	457,664
Level 3
Liabilities:
Other liabilities	15,000	24,000
Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	63,973	47,129
Recurring fair value measurements
Assets:
Total assets categorized within the fair value hierarchy	4,259,889	4,679,262
Recurring fair value measurements | Level 1
Assets:
Fixed maturities, trading	0	0
Other assets		0
Total assets categorized within the fair value hierarchy	322,534	388,285
Liabilities:
Other liabilities	0	0
Total liabilities categorized within the fair value hierarchy	0	0
Recurring fair value measurements | Level 1 | U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 1 | Financial
Assets:
Equity investments	9,850	6,615
Recurring fair value measurements | Level 1 | Utilities/Energy
Assets:
Equity investments	854
Recurring fair value measurements | Level 1 | Industrial
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 1 | Bond funds
Assets:
Equity investments	112,136	187,059
Recurring fair value measurements | Level 1 | All other
Assets:
Equity investments	15,876	17,778
Recurring fair value measurements | Level 1 | Short-term investments
Assets:
Short-term investments	181,937	174,944
Recurring fair value measurements | Level 1 | Other investments
Assets:
Short-term investments	1,881	1,889
Recurring fair value measurements | Level 2
Assets:
Fixed maturities, trading	43,434	43,670
Other assets		649
Total assets categorized within the fair value hierarchy	3,603,357	3,962,596
Liabilities:
Other liabilities	0	0
Total liabilities categorized within the fair value hierarchy	0	0
Recurring fair value measurements | Level 2 | U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	221,608	238,507
Recurring fair value measurements | Level 2 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	19,934	20,234
Recurring fair value measurements | Level 2 | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	439,450	519,196
Recurring fair value measurements | Level 2 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	1,717,479	1,851,427
Recurring fair value measurements | Level 2 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 2 | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	389,291	453,644
Recurring fair value measurements | Level 2 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	9,704	14,141
Recurring fair value measurements | Level 2 | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	194,090	231,483
Recurring fair value measurements | Level 2 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	413,989	451,459
Recurring fair value measurements | Level 2 | Financial
Assets:
Equity investments	2,219	855
Recurring fair value measurements | Level 2 | Utilities/Energy
Assets:
Equity investments	0
Recurring fair value measurements | Level 2 | Industrial
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 2 | Bond funds
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 2 | All other
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 2 | Short-term investments
Assets:
Short-term investments	63,376	42,043
Recurring fair value measurements | Level 2 | Other investments
Assets:
Short-term investments	88,783	95,288
Recurring fair value measurements | Level 3
Assets:
Fixed maturities, trading	0	0
Other assets		0
Total assets categorized within the fair value hierarchy	71,513	57,565
Liabilities:
Other liabilities	15,000	24,000
Total liabilities categorized within the fair value hierarchy	15,000	24,000
Recurring fair value measurements | Level 3 | U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	63,973	47,129
Recurring fair value measurements | Level 3 | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	249	297
Recurring fair value measurements | Level 3 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	0
Recurring fair value measurements | Level 3 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	2,705	6,205
Recurring fair value measurements | Level 3 | Financial
Assets:
Equity investments	303	0
Recurring fair value measurements | Level 3 | Utilities/Energy
Assets:
Equity investments	0
Recurring fair value measurements | Level 3 | Industrial
Assets:
Equity investments	2,500	2,500
Recurring fair value measurements | Level 3 | Bond funds
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 3 | All other
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 3 | Short-term investments
Assets:
Short-term investments	0	0
Recurring fair value measurements | Level 3 | Other investments
Assets:
Short-term investments	1,783	1,434
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, trading	43,434	43,670
Other assets		649
Total assets categorized within the fair value hierarchy	3,997,404	4,408,446
Liabilities:
Other liabilities	15,000	24,000
Total liabilities categorized within the fair value hierarchy	15,000	24,000
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	221,608	238,507
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	19,934	20,234
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	439,450	519,196
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	1,717,479	1,851,427
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	63,973	47,129
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	389,540	453,941
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	9,704	14,141
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	194,090	231,483
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	416,694	457,664
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Financial
Assets:
Equity investments	12,372	7,470
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Utilities/Energy
Assets:
Equity investments	854
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Industrial
Assets:
Equity investments	2,500	2,500
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Bond funds
Assets:
Equity investments	112,136	187,059
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | All other
Assets:
Equity investments	15,876	17,778
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Short-term investments
Assets:
Short-term investments	245,313	216,987
Recurring fair value measurements | Fair Value, Inputs, Level 1, 2 and 3 | Other investments
Assets:
Short-term investments	92,447	98,611
Recurring fair value measurements | Fair Value Measured at Net Asset Value Per Share | Equity investments | Investment in unconsolidated subsidiaries
Assets:
Total assets categorized within the fair value hierarchy	$ 262,485	$ 270,816