Investments - Gross Unrealized Losses and Related Fair Values of Available for Sale Securities (Details) $ in Thousands	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	858	519
Fair value, less than 12 months	$ 3,463,314	$ 2,004,842
Unrealized losses, less than 12 months	$ (312,320)	$ (28,445)
Number of securities, 12 months or greater | security	426	60
Fair value, 12 months or greater	$ 1,434,379	$ 166,248
Unrealized losses, 12 months or greater	$ (269,173)	$ (9,593)
Number of securities, total | security	1,284	579
Fair value, total	$ 4,897,693	$ 2,171,090
Unrealized losses, total	$ (581,493)	$ (38,038)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	14	14
Fair value, less than 12 months	$ 86,964	$ 101,602
Unrealized losses, less than 12 months	$ (21,370)	$ (1,165)
Number of securities, 12 months or greater | security	10	2
Fair value, 12 months or greater	$ 47,770	$ 6,937
Unrealized losses, 12 months or greater	$ (7,532)	$ (231)
Number of securities, total | security	24	16
Fair value, total	$ 134,734	$ 108,539
Unrealized losses, total	$ (28,902)	$ (1,396)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	43	20
Fair value, less than 12 months	$ 116,285	$ 32,721
Unrealized losses, less than 12 months	$ (14,231)	$ (401)
Number of securities, 12 months or greater | security	20	0
Fair value, 12 months or greater	$ 25,401	$ 0
Unrealized losses, 12 months or greater	$ (7,708)	$ 0
Number of securities, total | security	63	20
Fair value, total	$ 141,686	$ 32,721
Unrealized losses, total	$ (21,939)	$ (401)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	411	209
Fair value, less than 12 months	$ 1,769,547	$ 864,355
Unrealized losses, less than 12 months	$ (176,768)	$ (16,799)
Number of securities, 12 months or greater | security	203	34
Fair value, 12 months or greater	$ 701,936	$ 99,475
Unrealized losses, 12 months or greater	$ (173,769)	$ (8,087)
Number of securities, total | security	614	243
Fair value, total	$ 2,471,483	$ 963,830
Unrealized losses, total	$ (350,537)	$ (24,886)
RMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	124	57
Fair value, less than 12 months	$ 610,812	$ 365,476
Unrealized losses, less than 12 months	$ (46,117)	$ (6,749)
Number of securities, 12 months or greater | security	59	3
Fair value, 12 months or greater	$ 261,370	$ 1,543
Unrealized losses, 12 months or greater	$ (52,442)	$ (28)
Number of securities, total | security	183	60
Fair value, total	$ 872,182	$ 367,019
Unrealized losses, total	$ (98,559)	$ (6,777)
CMBS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	108	81
Fair value, less than 12 months	$ 469,100	$ 188,457
Unrealized losses, less than 12 months	$ (38,178)	$ (2,053)
Number of securities, 12 months or greater | security	55	9
Fair value, 12 months or greater	$ 121,277	$ 22,050
Unrealized losses, 12 months or greater	$ (14,368)	$ (1,015)
Number of securities, total | security	163	90
Fair value, total	$ 590,377	$ 210,507
Unrealized losses, total	$ (52,546)	$ (3,068)
CLO
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	94	84
Fair value, less than 12 months	$ 246,705	$ 313,380
Unrealized losses, less than 12 months	$ (10,271)	$ (675)
Number of securities, 12 months or greater | security	61	11
Fair value, 12 months or greater	$ 245,584	$ 35,612
Unrealized losses, 12 months or greater	$ (10,214)	$ (223)
Number of securities, total | security	155	95
Fair value, total	$ 492,289	$ 348,992
Unrealized losses, total	$ (20,485)	$ (898)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	61	54
Fair value, less than 12 months	$ 115,181	$ 138,851
Unrealized losses, less than 12 months	$ (3,603)	$ (603)
Number of securities, 12 months or greater | security	18	1
Fair value, 12 months or greater	$ 31,041	$ 631
Unrealized losses, 12 months or greater	$ (3,140)	$ (9)
Number of securities, total | security	79	55
Fair value, total	$ 146,222	$ 139,482
Unrealized losses, total	$ (6,743)	$ (612)
Mortgage insurance-linked notes
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	2
Fair value, less than 12 months	$ 43,745
Unrealized losses, less than 12 months	$ (1,639)
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	2
Fair value, total	$ 43,745
Unrealized losses, total	$ (1,639)
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	$ 4,975
Unrealized losses, less than 12 months	$ (143)
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	$ 4,975
Unrealized losses, total	$ (143)