Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Assets:
Fixed maturities available for sale, at fair value	$ 3,582,207	$ 3,493,597
Fixed maturities, trading	53,157	48,324
Equity investments	130,158	151,295
U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	243,903	243,525
U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	14,894	18,724
State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	446,601	454,381
Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	478,799	430,137
Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	6,727	8,387
Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	201,786	189,474
Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	461,722	398,395
Level 3
Liabilities:
Other liabilities	0	6,500
Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	81,062	82,377
Recurring fair value measurements
Assets:
Total assets categorized within the fair value hierarchy	4,254,884	4,240,936
Recurring fair value measurements | Total Fair Value
Assets:
Fixed maturities, trading	53,157	48,324
Other assets	6,094	3,876
Total assets categorized within the fair value hierarchy	4,028,615	3,995,481
Liabilities:
Other liabilities	6,680	10,530
Total liabilities categorized within the fair value hierarchy	6,680	10,530
Recurring fair value measurements | Total Fair Value | U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	243,903	243,525
Recurring fair value measurements | Total Fair Value | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	14,894	18,724
Recurring fair value measurements | Total Fair Value | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	446,601	454,381
Recurring fair value measurements | Total Fair Value | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	1,646,713	1,668,197
Recurring fair value measurements | Total Fair Value | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	81,062	82,377
Recurring fair value measurements | Total Fair Value | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	478,799	430,137
Recurring fair value measurements | Total Fair Value | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	6,727	8,387
Recurring fair value measurements | Total Fair Value | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	201,786	189,474
Recurring fair value measurements | Total Fair Value | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	461,722	398,395
Recurring fair value measurements | Total Fair Value | Financial
Assets:
Equity investments	11,589	12,042
Recurring fair value measurements | Total Fair Value | Utilities/Energy
Assets:
Equity investments	724	1,256
Recurring fair value measurements | Total Fair Value | Industrial
Assets:
Equity investments	5,233	4,946
Recurring fair value measurements | Total Fair Value | Bond funds
Assets:
Equity investments	101,243	114,901
Recurring fair value measurements | Total Fair Value | All other
Assets:
Equity investments	11,369	18,150
Recurring fair value measurements | Total Fair Value | Short-term investments
Assets:
Short-term investments	254,922	235,785
Recurring fair value measurements | Total Fair Value | Other investments
Assets:
Short-term investments	2,077	62,604
Recurring fair value measurements | Level 1
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	307,834	307,270
Liabilities:
Other liabilities	6,680	4,030
Total liabilities categorized within the fair value hierarchy	6,680	4,030
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	9,006	9,464
Recurring fair value measurements | Level 1 | Utilities/Energy
Assets:
Equity investments	724	1,256
Recurring fair value measurements | Level 1 | Industrial
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 1 | Bond funds
Assets:
Equity investments	101,243	114,901
Recurring fair value measurements | Level 1 | All other
Assets:
Equity investments	11,369	18,150
Recurring fair value measurements | Level 1 | Short-term investments
Assets:
Short-term investments	185,492	163,499
Recurring fair value measurements | Level 1 | Other investments
Assets:
Short-term investments	0	0
Recurring fair value measurements | Level 2
Assets:
Fixed maturities, trading	53,157	48,324
Other assets	6,094	3,876
Total assets categorized within the fair value hierarchy	3,629,939	3,591,057
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	243,903	243,525
Recurring fair value measurements | Level 2 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	14,894	18,724
Recurring fair value measurements | Level 2 | State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	446,601	454,381
Recurring fair value measurements | Level 2 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities available for sale, at fair value	1,646,713	1,668,197
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	478,799	429,883
Recurring fair value measurements | Level 2 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	6,727	8,387
Recurring fair value measurements | Level 2 | Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	201,786	188,464
Recurring fair value measurements | Level 2 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	457,948	395,245
Recurring fair value measurements | Level 2 | Financial
Assets:
Equity investments	2,310	2,287
Recurring fair value measurements | Level 2 | Utilities/Energy
Assets:
Equity investments	0	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	69,430	72,286
Recurring fair value measurements | Level 2 | Other investments
Assets:
Short-term investments	1,577	57,478
Recurring fair value measurements | Level 3
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	90,842	97,154
Liabilities:
Other liabilities	0	6,500
Total liabilities categorized within the fair value hierarchy	0	6,500
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	81,062	82,377
Recurring fair value measurements | Level 3 | Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	0	254
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	1,010
Recurring fair value measurements | Level 3 | Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	3,774	3,150
Recurring fair value measurements | Level 3 | Financial
Assets:
Equity investments	273	291
Recurring fair value measurements | Level 3 | Utilities/Energy
Assets:
Equity investments	0	0
Recurring fair value measurements | Level 3 | Industrial
Assets:
Equity investments	5,233	4,946
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	500	5,126
Recurring fair value measurements | Fair Value Measured at Net Asset Value Per Share | Equity investments
Assets:
Total assets categorized within the fair value hierarchy	$ 226,269	$ 245,455