Investments - Schedule of Available-For-Sale Securities in a Gross Unrealized Loss Position by Length of Time (Details) $ in Thousands	Sep. 30, 2022 USD ($) holding	Dec. 31, 2021 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 649,184	$ 330,697
12 months or longer	106,235	17,112
Total	755,419	347,809
Unrealized losses
Less than 12 months	51,725	3,801
12 months or longer	14,782	434
Total	$ 66,507	$ 4,235
No. of holdings | holding	770	366
Non-investment grade
Fair value
Less than 12 months	$ 100,984	$ 45,279
12 months or longer	9,057	6,110
Total	110,041	51,389
Unrealized losses
Less than 12 months	11,557	405
12 months or longer	1,739	415
Total	$ 13,296	$ 820
No. of holdings | holding	747	363
Corporate debt securities
Fair value
Less than 12 months	$ 488,178	$ 179,281
12 months or longer	52,867	12,494
Total	541,045	191,775
Unrealized losses
Less than 12 months	37,243	1,912
12 months or longer	7,432	583
Total	$ 44,675	$ 2,495
No. of holdings | holding	1,030	441
Collateralized debt obligations
Fair value
Less than 12 months	$ 67,482	$ 64,270
12 months or longer	31,984	9,370
Total	99,466	73,640
Unrealized losses
Less than 12 months	3,368	278
12 months or longer	1,905	60
Total	$ 5,273	$ 338
No. of holdings | holding	159	104
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 56,265	$ 28,001
12 months or longer	6,174	917
Total	62,439	28,918
Unrealized losses
Less than 12 months	6,480	595
12 months or longer	1,335	182
Total	$ 7,815	$ 777
No. of holdings | holding	123	61
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 104,610	$ 89,460
12 months or longer	23,145	441
Total	127,755	89,901
Unrealized losses
Less than 12 months	13,096	1,278
12 months or longer	5,635	24
Total	$ 18,731	$ 1,302
No. of holdings | holding	157	98
Other debt securities
Fair value
Less than 12 months	$ 21,428	$ 14,576
12 months or longer	1,122	0
Total	22,550	14,576
Unrealized losses
Less than 12 months	2,034	136
12 months or longer	214	0
Total	$ 2,248	$ 136
No. of holdings | holding	45	24
U.S. Treasury
Fair value
Less than 12 months	$ 12,205	$ 388
12 months or longer	0	0
Total	12,205	388
Unrealized losses
Less than 12 months	1,061	7
12 months or longer	0	0
Total	$ 1,061	$ 7
No. of holdings | holding	3	1
Available-for-sale securities
Fair value
Less than 12 months	$ 750,168	$ 375,976
12 months or longer	115,292	23,222
Total	865,460	399,198
Unrealized losses
Less than 12 months	63,282	4,206
12 months or longer	16,521	849
Total	$ 79,803	$ 5,055
No. of holdings | holding	1,517	729