Investments - Gross Unrealized Losses and Related Fair Values of Available for Sale Securities (Details) $ in Thousands	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	519	194
Fair value, less than 12 months	$ 2,004,842	$ 679,631
Unrealized losses, less than 12 months	$ (28,445)	$ (12,101)
Number of securities, 12 months or greater | security	60	36
Fair value, 12 months or greater	$ 166,248	$ 158,852
Unrealized losses, 12 months or greater	$ (9,593)	$ (2,056)
Number of securities, total | security	579	230
Fair value, total	$ 2,171,090	$ 838,483
Unrealized losses, total	$ (38,038)	$ (14,157)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	14	4
Fair value, less than 12 months	$ 101,602	$ 90,591
Unrealized losses, less than 12 months	$ (1,165)	$ (3,611)
Number of securities, 12 months or greater | security	2	0
Fair value, 12 months or greater	$ 6,937	$ 0
Unrealized losses, 12 months or greater	$ (231)	$ 0
Number of securities, total | security	16	4
Fair value, total	$ 108,539	$ 90,591
Unrealized losses, total	$ (1,396)	$ (3,611)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	20	4
Fair value, less than 12 months	$ 32,721	$ 9,626
Unrealized losses, less than 12 months	$ (401)	$ (100)
Number of securities, 12 months or greater | security	0	0
Fair value, 12 months or greater	$ 0	$ 0
Unrealized losses, 12 months or greater	$ 0	$ 0
Number of securities, total | security	20	4
Fair value, total	$ 32,721	$ 9,626
Unrealized losses, total	$ (401)	$ (100)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	209	60
Fair value, less than 12 months	$ 864,355	$ 174,848
Unrealized losses, less than 12 months	$ (16,799)	$ (3,758)
Number of securities, 12 months or greater | security	34	0
Fair value, 12 months or greater	$ 99,475	$ 0
Unrealized losses, 12 months or greater	$ (8,087)	$ 0
Number of securities, total | security	243	60
Fair value, total	$ 963,830	$ 174,848
Unrealized losses, total	$ (24,886)	$ (3,758)
RMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	57	5
Fair value, less than 12 months	$ 365,476	$ 42,003
Unrealized losses, less than 12 months	$ (6,749)	$ (305)
Number of securities, 12 months or greater | security	3	2
Fair value, 12 months or greater	$ 1,543	$ 915
Unrealized losses, 12 months or greater	$ (28)	$ (9)
Number of securities, total | security	60	7
Fair value, total	$ 367,019	$ 42,918
Unrealized losses, total	$ (6,777)	$ (314)
CMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	81	43
Fair value, less than 12 months	$ 188,457	$ 118,345
Unrealized losses, less than 12 months	$ (2,053)	$ (3,035)
Number of securities, 12 months or greater | security	9	6
Fair value, 12 months or greater	$ 22,050	$ 8,312
Unrealized losses, 12 months or greater	$ (1,015)	$ (266)
Number of securities, total | security	90	49
Fair value, total	$ 210,507	$ 126,657
Unrealized losses, total	$ (3,068)	$ (3,301)
CLO
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	84	52
Fair value, less than 12 months	$ 313,380	$ 173,459
Unrealized losses, less than 12 months	$ (675)	$ (970)
Number of securities, 12 months or greater | security	11	25
Fair value, 12 months or greater	$ 35,612	$ 137,506
Unrealized losses, 12 months or greater	$ (223)	$ (1,671)
Number of securities, total | security	95	77
Fair value, total	$ 348,992	$ 310,965
Unrealized losses, total	$ (898)	$ (2,641)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	54	26
Fair value, less than 12 months	$ 138,851	$ 70,759
Unrealized losses, less than 12 months	$ (603)	$ (322)
Number of securities, 12 months or greater | security	1	3
Fair value, 12 months or greater	$ 631	$ 12,119
Unrealized losses, 12 months or greater	$ (9)	$ (110)
Number of securities, total | security	55	29
Fair value, total	$ 139,482	$ 82,878
Unrealized losses, total	$ (612)	$ (432)