Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value by Hierarchy Level (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	$ 141,614	$ 203,693
Securitized residential mortgage loans held for investment at fair value	353,078
Securitized nonrecourse debt	344,904
Other invested assets—at fair value	7,809	8,625
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	6,495,179	6,084,225
Derivative assets	2,830	1,913
Mortgage servicing rights	1,714
Securitized residential mortgage loans held for investment at fair value	353,078
Total assets at fair value	6,994,415	6,289,831
Derivative Liabilities	2,842	1,509
Securitized nonrecourse debt	344,904
Total liabilities at fair value	347,746	1,509
Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	581,785	574,337
Derivative assets	0	0
Mortgage servicing rights	0
Securitized residential mortgage loans held for investment at fair value	0
Total assets at fair value	600,361	660,038
Derivative Liabilities	0	0
Securitized nonrecourse debt	0
Total liabilities at fair value	0	0
Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,901,040	5,500,192
Derivative assets	2,830	1,912
Mortgage servicing rights	0
Securitized residential mortgage loans held for investment at fair value	353,078
Total assets at fair value	6,379,986	5,620,096
Derivative Liabilities	94	817
Securitized nonrecourse debt	344,904
Total liabilities at fair value	344,998	817
Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	12,354	9,696
Derivative assets	0	1
Mortgage servicing rights	1,714
Securitized residential mortgage loans held for investment at fair value	0
Total assets at fair value	14,068	9,697
Derivative Liabilities	2,748	692
Securitized nonrecourse debt	0
Total liabilities at fair value	2,748	692
Loaned securities | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities		9,803
Loaned securities | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	13
Loaned securities | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	121,819	117,992
Loaned securities | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	1,206
Loaned securities | Level I | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities		9,803
Loaned securities | Level I | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0
Loaned securities | Level I | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0	0
Loaned securities | Level I | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0
Loaned securities | Level II | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities		0
Loaned securities | Level II | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	13
Loaned securities | Level II | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	121,819	117,992
Loaned securities | Level II | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	1,206
Loaned securities | Level III | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities		0
Loaned securities | Level III | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0
Loaned securities | Level III | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0	0
Loaned securities | Level III | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0
Fixed-maturities available for sale | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,292,480	5,188,228
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	136,262	134,593
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	160,289	142,785
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	2,553,145	2,511,905
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	1,058,454	1,014,071
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	473,312	558,383
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | CLO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	467,761	487,849
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	395,603	284,559
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | Foreign government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		5,087
Fixed-maturities available for sale | Fair Value, Measurements, Recurring | Mortgage insurance-linked notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	47,654	48,996
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	127,300	124,734
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	127,300	124,734
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | CLO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | Foreign government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		0
Fixed-maturities available for sale | Level I | Fair Value, Measurements, Recurring | Mortgage insurance-linked notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,165,180	5,063,494
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	8,962	9,859
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	160,289	142,785
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	2,553,145	2,511,905
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	1,058,454	1,014,071
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	473,312	558,383
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | CLO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	467,761	487,849
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	395,603	284,559
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | Foreign government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		5,087
Fixed-maturities available for sale | Level II | Fair Value, Measurements, Recurring | Mortgage insurance-linked notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	47,654	48,996
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | CLO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | Foreign government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		0
Fixed-maturities available for sale | Level III | Fair Value, Measurements, Recurring | Mortgage insurance-linked notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	89,272	106,423
Trading securities | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	53,592	70,844
Trading securities | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	25,465	24,913
Trading securities | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,346	5,930
Trading securities | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	4,869	4,736
Trading securities | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level I | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level I | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level I | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level I | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	89,272	106,423
Trading securities | Level II | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	53,592	70,844
Trading securities | Level II | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	25,465	24,913
Trading securities | Level II | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,346	5,930
Trading securities | Level II | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	4,869	4,736
Trading securities | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level III | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level III | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level III | Fair Value, Measurements, Recurring | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Trading securities | Level III | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Equity securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	145,717	89,057
Equity securities | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	135,556	81,170
Equity securities | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	3,615	5,387
Equity securities | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	6,546	2,500
Equity securities | Loaned securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	18,576	75,898
Equity securities | Loaned securities | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	18,576	75,898
Equity securities | Loaned securities | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0	0
Equity securities | Loaned securities | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loaned securities	0	0
Residential mortgage loans held for sale | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	529,517	32,755
Residential mortgage loans held for sale | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Residential mortgage loans held for sale | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	529,517	32,755
Residential mortgage loans held for sale | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Other invested assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,808	7,196
Other invested assets | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Other invested assets | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0
Other invested assets | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	5,808	7,196
Short-term investments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	432,385	660,566
Short-term investments | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	2,200	2,700
Short-term investments | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	50,512	150,930
Short-term investments | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		1,347
Short-term investments | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	9,789	1,158
Short-term investments | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	50,955	135,998
Short-term investments | Fair Value, Measurements, Recurring | Money market instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	318,929	368,433
Short-term investments | Level I | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	318,929	368,433
Short-term investments | Level I | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level I | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level I | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		0
Short-term investments | Level I | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level I | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level I | Fair Value, Measurements, Recurring | Money market instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	318,929	368,433
Short-term investments | Level II | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	113,456	292,133
Short-term investments | Level II | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	2,200	2,700
Short-term investments | Level II | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	50,512	150,930
Short-term investments | Level II | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		1,347
Short-term investments | Level II | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	9,789	1,158
Short-term investments | Level II | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	50,955	135,998
Short-term investments | Level II | Fair Value, Measurements, Recurring | Money market instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring | State and municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value		0
Short-term investments | Level III | Fair Value, Measurements, Recurring | Other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring | Other investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Short-term investments | Level III | Fair Value, Measurements, Recurring | Money market instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments at fair value	0	0
Partnership investments | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets—at fair value	$ 2,000	$ 1,000