Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2021 USD ($) holding	Dec. 31, 2020 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 330,697	$ 86,807
12 months or longer	17,112	10,899
Total	347,809	97,706
Unrealized losses
Less than 12 months	3,801	561
12 months or longer	434	99
Total	$ 4,235	$ 660
No. of holdings | holding	366	119
Non-investment grade
Fair value
Less than 12 months	$ 45,279	$ 28,686
12 months or longer	6,110	7,952
Total	51,389	36,638
Unrealized losses
Less than 12 months	405	593
12 months or longer	415	870
Total	$ 820	$ 1,463
No. of holdings | holding	363	251
Corporate debt securities
Fair value
Less than 12 months	$ 179,281	$ 39,693
12 months or longer	12,494	7,952
Total	191,775	47,645
Unrealized losses
Less than 12 months	1,912	644
12 months or longer	583	870
Total	$ 2,495	$ 1,514
No. of holdings | holding	441	257
Collateralized debt obligations
Fair value
Less than 12 months	$ 64,270	$ 50,036
12 months or longer	9,370	10,899
Total	73,640	60,935
Unrealized losses
Less than 12 months	278	232
12 months or longer	60	99
Total	$ 338	$ 331
No. of holdings | holding	104	65
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 28,001	$ 16,582
12 months or longer	917	0
Total	28,918	16,582
Unrealized losses
Less than 12 months	595	235
12 months or longer	182	0
Total	$ 777	$ 235
No. of holdings | holding	61	31
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 89,460	$ 8,163
12 months or longer	441	0
Total	89,901	8,163
Unrealized losses
Less than 12 months	1,278	34
12 months or longer	24	0
Total	$ 1,302	$ 34
No. of holdings | holding	98	13
Other debt securities
Fair value
Less than 12 months	$ 14,576	$ 1,019
12 months or longer	0	0
Total	14,576	1,019
Unrealized losses
Less than 12 months	136	9
12 months or longer	0	0
Total	$ 136	$ 9
No. of holdings | holding	24	4
U.S. Treasury
Fair value
Less than 12 months	$ 388
12 months or longer	0
Total	388
Unrealized losses
Less than 12 months	7
12 months or longer	0
Total	$ 7
No. of holdings | holding	1
Available-for-sale securities
Fair value
Less than 12 months	$ 375,976	$ 115,493
12 months or longer	23,222	18,851
Total	399,198	134,344
Unrealized losses
Less than 12 months	4,206	1,154
12 months or longer	849	969
Total	$ 5,055	$ 2,123
No. of holdings | holding	729	370