Investments - Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) $ in Thousands	Jun. 30, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	1,102	519
Fair value, less than 12 months	$ 4,331,570	$ 2,004,842
Unrealized losses, less than 12 months	$ (330,469)	$ (28,445)
Number of securities, 12 months or greater | security	141	60
Fair value, 12 months or greater	$ 484,275	$ 166,248
Unrealized losses, 12 months or greater	$ (89,607)	$ (9,593)
Number of securities, total | security	1,243	579
Fair value, total	$ 4,815,845	$ 2,171,090
Unrealized losses, total	$ (420,076)	$ (38,038)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	19	14
Fair value, less than 12 months	$ 122,570	$ 101,602
Unrealized losses, less than 12 months	$ (17,028)	$ (1,165)
Number of securities, 12 months or greater | security	5	2
Fair value, 12 months or greater	$ 20,027	$ 6,937
Unrealized losses, 12 months or greater	$ (1,322)	$ (231)
Number of securities, total | security	24	16
Fair value, total	$ 142,597	$ 108,539
Unrealized losses, total	$ (18,350)	$ (1,396)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	51	20
Fair value, less than 12 months	$ 103,028	$ 32,721
Unrealized losses, less than 12 months	$ (12,050)	$ (401)
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	51	20
Fair value, total	$ 103,028	$ 32,721
Unrealized losses, total	$ (12,050)	$ (401)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	532	209
Fair value, less than 12 months	$ 2,308,451	$ 864,355
Unrealized losses, less than 12 months	$ (214,471)	$ (16,799)
Number of securities, 12 months or greater | security	71	34
Fair value, 12 months or greater	$ 198,415	$ 99,475
Unrealized losses, 12 months or greater	$ (57,265)	$ (8,087)
Number of securities, total | security	603	243
Fair value, total	$ 2,506,866	$ 963,830
Unrealized losses, total	$ (271,736)	$ (24,886)
RMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	142	57
Fair value, less than 12 months	$ 607,722	$ 365,476
Unrealized losses, less than 12 months	$ (43,891)	$ (6,749)
Number of securities, 12 months or greater | security	22	3
Fair value, 12 months or greater	$ 128,182	$ 1,543
Unrealized losses, 12 months or greater	$ (20,026)	$ (28)
Number of securities, total | security	164	60
Fair value, total	$ 735,904	$ 367,019
Unrealized losses, total	$ (63,917)	$ (6,777)
CMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	144	81
Fair value, less than 12 months	$ 558,045	$ 188,457
Unrealized losses, less than 12 months	$ (24,441)	$ (2,053)
Number of securities, 12 months or greater | security	17	9
Fair value, 12 months or greater	$ 43,123	$ 22,050
Unrealized losses, 12 months or greater	$ (6,566)	$ (1,015)
Number of securities, total | security	161	90
Fair value, total	$ 601,168	$ 210,507
Unrealized losses, total	$ (31,007)	$ (3,068)
CLO
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	136	84
Fair value, less than 12 months	$ 413,093	$ 313,380
Unrealized losses, less than 12 months	$ (13,506)	$ (675)
Number of securities, 12 months or greater | security	22	11
Fair value, 12 months or greater	$ 89,722	$ 35,612
Unrealized losses, 12 months or greater	$ (4,159)	$ (223)
Number of securities, total | security	158	95
Fair value, total	$ 502,815	$ 348,992
Unrealized losses, total	$ (17,665)	$ (898)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	74	54
Fair value, less than 12 months	$ 161,012	$ 138,851
Unrealized losses, less than 12 months	$ (3,933)	$ (603)
Number of securities, 12 months or greater | security	4	1
Fair value, 12 months or greater	$ 4,806	$ 631
Unrealized losses, 12 months or greater	$ (269)	$ (9)
Number of securities, total | security	78	55
Fair value, total	$ 165,818	$ 139,482
Unrealized losses, total	$ (4,202)	$ (612)
Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	3
Fair value, less than 12 months	$ 52,600
Unrealized losses, less than 12 months	$ (1,085)
Number of securities, 12 months or greater | security	0
Fair value, 12 months or greater	$ 0
Unrealized losses, 12 months or greater	$ 0
Number of securities, total | security	3
Fair value, total	$ 52,600
Unrealized losses, total	$ (1,085)
Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	1
Fair value, less than 12 months	$ 5,049
Unrealized losses, less than 12 months	$ (64)
Number of securities, 12 months or greater | security	0
Fair value, 12 months or greater	$ 0
Unrealized losses, 12 months or greater	$ 0
Number of securities, total | security	1
Fair value, total	$ 5,049
Unrealized losses, total	$ (64)