Fair Value Measurement (Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Fixed maturities, available-for-sale	$ 3,544,137	$ 3,493,597
Fixed maturities, trading	50,106	48,324
Equity investments	137,914	151,295
Level 3
Liabilities:
Other liabilities	6,500	6,500
U.S. Treasury obligations
Assets:
Fixed maturities, available-for-sale	240,889	243,525
U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available-for-sale	18,927	18,724
State and municipal bonds
Assets:
Fixed maturities, available-for-sale	474,265	454,381
Corporate debt, limited observable inputs | Level 3
Assets:
Fixed maturities, available-for-sale	66,208	82,377
Residential mortgage-backed securities
Assets:
Fixed maturities, available-for-sale	450,052	430,137
Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available-for-sale	7,950	8,387
Other commercial mortgage-backed securities
Assets:
Fixed maturities, available-for-sale	229,029	189,474
Other asset-backed securities
Assets:
Fixed maturities, available-for-sale	408,973	398,395
Recurring
Assets:
Total assets categorized within the fair value hierarchy	4,225,707	4,240,936
Recurring | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, trading	50,106	48,324
Other assets	7,674	3,876
Total assets categorized within the fair value hierarchy	3,979,564	3,995,481
Liabilities:
Other liabilities	15,550	10,530
Total liabilities categorized within the fair value hierarchy	15,550	10,530
Recurring | Level 1
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	233,085	307,270
Liabilities:
Other liabilities	9,050	4,030
Total liabilities categorized within the fair value hierarchy	9,050	4,030
Recurring | Level 2
Assets:
Fixed maturities, trading	50,106	48,324
Other assets	7,674	3,876
Total assets categorized within the fair value hierarchy	3,672,154	3,591,057
Liabilities:
Other liabilities	0	0
Total liabilities categorized within the fair value hierarchy	0	0
Recurring | Level 3
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	74,325	97,154
Liabilities:
Other liabilities	6,500	6,500
Total liabilities categorized within the fair value hierarchy	6,500	6,500
Recurring | U.S. Treasury obligations | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	240,889	243,525
Recurring | U.S. Treasury obligations | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | U.S. Treasury obligations | Level 2
Assets:
Fixed maturities, available-for-sale	240,889	243,525
Recurring | U.S. Treasury obligations | Level 3
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | U.S. Government-sponsored enterprise obligations | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	18,927	18,724
Recurring | U.S. Government-sponsored enterprise obligations | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | U.S. Government-sponsored enterprise obligations | Level 2
Assets:
Fixed maturities, available-for-sale	18,927	18,724
Recurring | U.S. Government-sponsored enterprise obligations | Level 3
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | State and municipal bonds | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	474,265	454,381
Recurring | State and municipal bonds | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | State and municipal bonds | Level 2
Assets:
Fixed maturities, available-for-sale	474,265	454,381
Recurring | State and municipal bonds | Level 3
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Corporate debt, multiple observable inputs | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	1,647,844	1,668,197
Recurring | Corporate debt, multiple observable inputs | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Corporate debt, multiple observable inputs | Level 2
Assets:
Fixed maturities, available-for-sale	1,647,844	1,668,197
Recurring | Corporate debt, multiple observable inputs | Level 3
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Corporate debt, limited observable inputs | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	66,208	82,377
Recurring | Corporate debt, limited observable inputs | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Corporate debt, limited observable inputs | Level 2
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Corporate debt, limited observable inputs | Level 3
Assets:
Fixed maturities, available-for-sale	66,208	82,377
Recurring | Residential mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	450,052	430,137
Recurring | Residential mortgage-backed securities | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Residential mortgage-backed securities | Level 2
Assets:
Fixed maturities, available-for-sale	450,052	429,883
Recurring | Residential mortgage-backed securities | Level 3
Assets:
Fixed maturities, available-for-sale	0	254
Recurring | Agency commercial mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	7,950	8,387
Recurring | Agency commercial mortgage-backed securities | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Agency commercial mortgage-backed securities | Level 2
Assets:
Fixed maturities, available-for-sale	7,950	8,387
Recurring | Agency commercial mortgage-backed securities | Level 3
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Other commercial mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	229,029	189,474
Recurring | Other commercial mortgage-backed securities | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Other commercial mortgage-backed securities | Level 2
Assets:
Fixed maturities, available-for-sale	229,029	188,464
Recurring | Other commercial mortgage-backed securities | Level 3
Assets:
Fixed maturities, available-for-sale	0	1,010
Recurring | Other asset-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, available-for-sale	408,973	398,395
Recurring | Other asset-backed securities | Level 1
Assets:
Fixed maturities, available-for-sale	0	0
Recurring | Other asset-backed securities | Level 2
Assets:
Fixed maturities, available-for-sale	406,832	395,245
Recurring | Other asset-backed securities | Level 3
Assets:
Fixed maturities, available-for-sale	2,141	3,150
Recurring | Financial | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	12,308	12,042
Recurring | Financial | Level 1
Assets:
Equity investments	9,750	9,464
Recurring | Financial | Level 2
Assets:
Equity investments	2,270	2,287
Recurring | Financial | Level 3
Assets:
Equity investments	288	291
Recurring | Utilities/Energy | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	1,258	1,256
Recurring | Utilities/Energy | Level 1
Assets:
Equity investments	1,258	1,256
Recurring | Utilities/Energy | Level 2
Assets:
Equity investments	0	0
Recurring | Utilities/Energy | Level 3
Assets:
Equity investments	0	0
Recurring | Industrial | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	4,946	4,946
Recurring | Industrial | Level 1
Assets:
Equity investments	0	0
Recurring | Industrial | Level 2
Assets:
Equity investments	0	0
Recurring | Industrial | Level 3
Assets:
Equity investments	4,946	4,946
Recurring | Bond funds | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	101,571	114,901
Recurring | Bond funds | Level 1
Assets:
Equity investments	101,571	114,901
Recurring | Bond funds | Level 2
Assets:
Equity investments	0	0
Recurring | Bond funds | Level 3
Assets:
Equity investments	0	0
Recurring | All other | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	17,831	18,150
Recurring | All other | Level 1
Assets:
Equity investments	17,831	18,150
Recurring | All other | Level 2
Assets:
Equity investments	0	0
Recurring | All other | Level 3
Assets:
Equity investments	0	0
Recurring | Short-term investments | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Short-term and other investments	184,001	235,785
Recurring | Short-term investments | Level 1
Assets:
Short-term and other investments	102,675	163,499
Recurring | Short-term investments | Level 2
Assets:
Short-term and other investments	81,326	72,286
Recurring | Short-term investments | Level 3
Assets:
Short-term and other investments	0	0
Recurring | Other investments | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Short-term and other investments	55,732	62,604
Recurring | Other investments | Level 1
Assets:
Short-term and other investments	0	0
Recurring | Other investments | Level 2
Assets:
Short-term and other investments	54,990	57,478
Recurring | Other investments | Level 3
Assets:
Short-term and other investments	742	5,126
Recurring | Equity investments | Fair Value Measured at Net Asset Value Per Share | Investment in unconsolidated subsidiaries
Assets:
Total assets categorized within the fair value hierarchy	$ 246,143	$ 245,455