Fair Value of Financial Instruments - Fair Value Assets Liabilities by Hierarchy Level (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value by Hierarchy Level [Line Items]
Loaned securities	$ 203,693	$ 112,139
Other invested assets	$ 8,625	$ 5,511
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other assets (Note 9)	Other liabilities
Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	$ 6,084,225	$ 5,692,276
Derivative assets	1,913	11
Total assets at fair value	6,289,831	5,804,426
Derivative Liabilities	1,509	4,900
Total liabilities at fair value	1,509	4,900
Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,188,228	5,017,711
Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	106,423	115,665
Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	89,057	148,965
Mortgage loans held for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	32,755	3,549
Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	7,196	4,296
Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	660,566	402,090
Partnership investment | Carrying Amount
Fair Value by Hierarchy Level [Line Items]
Other invested assets	1,000	1,000
Level I | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	574,337	520,167
Derivative assets	0	0
Total assets at fair value	660,038	584,721
Derivative Liabilities	0	0
Total liabilities at fair value	0	0
Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	124,734	140,011
Level I | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level I | Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	81,170	138,716
Level I | Mortgage loans held for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level I | Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	368,433	241,440
Level II | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,500,192	5,165,313
Derivative assets	1,912	11
Total assets at fair value	5,620,096	5,212,909
Derivative Liabilities	817	42
Total liabilities at fair value	817	42
Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,063,494	4,877,700
Level II | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	106,423	115,665
Level II | Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,387	7,749
Level II | Mortgage loans held for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	32,755	3,549
Level II | Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	292,133	160,650
Level III | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	9,696	6,796
Derivative assets	1	0
Total assets at fair value	9,697	6,796
Derivative Liabilities	692	4,858
Total liabilities at fair value	692	4,858
Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level III | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level III | Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	2,500	2,500
Level III | Mortgage loans held for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Level III | Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	7,196	4,296
Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Loaned securities
Fair Value by Hierarchy Level [Line Items]
Loaned securities	127,000
Loaned securities | Equity securities
Fair Value by Hierarchy Level [Line Items]
Loaned securities	76,000
Loaned securities | Short-term investments
Fair Value by Hierarchy Level [Line Items]
Loaned securities	1,000
U.S. government and agency securities | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	134,593	145,442
U.S. government and agency securities | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	124,734	140,011
U.S. government and agency securities | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	9,859	5,431
U.S. government and agency securities | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
U.S. government and agency securities | Loaned securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	9,803
U.S. government and agency securities | Loaned securities | Level I | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	9,803
U.S. government and agency securities | Loaned securities | Level II | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0
U.S. government and agency securities | Loaned securities | Level III | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0
State and municipal obligations | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	142,785	142,386
State and municipal obligations | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	70,844	70,511
State and municipal obligations | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	2,700	2,785
State and municipal obligations | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
State and municipal obligations | Level I | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
State and municipal obligations | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
State and municipal obligations | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	142,785	142,386
State and municipal obligations | Level II | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	70,844	70,511
State and municipal obligations | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	2,700	2,785
State and municipal obligations | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
State and municipal obligations | Level III | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
State and municipal obligations | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	2,511,905	2,490,582
Corporate bonds and notes | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	24,913	32,827
Corporate bonds and notes | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	150,930	42,385
Corporate bonds and notes | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Level I | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	2,511,905	2,490,582
Corporate bonds and notes | Level II | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	24,913	32,827
Corporate bonds and notes | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	150,930	42,385
Corporate bonds and notes | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Level III | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Corporate bonds and notes | Loaned securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	117,992	47,585
Corporate bonds and notes | Loaned securities | Level I | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0	0
Corporate bonds and notes | Loaned securities | Level II | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	117,992	47,585
Corporate bonds and notes | Loaned securities | Level III | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0	0
RMBS | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,014,071	928,399
RMBS | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,930	6,847
RMBS | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
RMBS | Level I | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
RMBS | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,014,071	928,399
RMBS | Level II | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,930	6,847
RMBS | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
RMBS | Level III | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CMBS | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	558,383	593,357
CMBS | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	4,736	5,480
CMBS | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,347
CMBS | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CMBS | Level I | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CMBS | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0
CMBS | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	558,383	593,357
CMBS | Level II | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	4,736	5,480
CMBS | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,347
CMBS | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CMBS | Level III | Trading securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CMBS | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0
CLO | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	487,849	498,192
CLO | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
CLO | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	487,849	498,192
CLO | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Other ABS | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	284,559	161,359
Other ABS | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,158
Other ABS | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Other ABS | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0
Other ABS | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	284,559	161,359
Other ABS | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	1,158
Other ABS | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Other ABS | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0
Foreign government and agency securities | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,087	4,975
Foreign government and agency securities | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Foreign government and agency securities | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	5,087	4,975
Foreign government and agency securities | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Mortgage insurance-linked notes | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	48,996	53,019
Mortgage insurance-linked notes | Level I | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Mortgage insurance-linked notes | Level II | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	48,996	53,019
Mortgage insurance-linked notes | Level III | Total fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Equity securities | Loaned securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	75,898	64,554
Equity securities | Loaned securities | Level I | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	75,898	64,554
Equity securities | Loaned securities | Level II | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0	0
Equity securities | Loaned securities | Level III | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Loaned securities	0	0
Other investments | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	135,998	115,480
Other investments | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Other investments | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	135,998	115,480
Other investments | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Money market instruments | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	368,433	241,440
Money market instruments | Level I | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	368,433	241,440
Money market instruments | Level II | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	0	0
Money market instruments | Level III | Short-term investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total investments at fair value	$ 0	$ 0