Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2021 USD ($) holding	Dec. 31, 2020 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 140,765	$ 86,807
12 months or longer	17,262	10,899
Total	158,027	97,706
Unrealized losses
Less than 12 months	1,212	561
12 months or longer	107	99
Total	$ 1,319	$ 660
No. of holdings | holding	174	119
Non-investment grade
Fair value
Less than 12 months	$ 28,468	$ 28,686
12 months or longer	8,559	7,952
Total	37,027	36,638
Unrealized losses
Less than 12 months	185	593
12 months or longer	366	870
Total	$ 551	$ 1,463
No. of holdings | holding	262	251
Available-for-sale securities
Fair value
Less than 12 months	$ 169,233	$ 115,493
12 months or longer	25,821	18,851
Total	195,054	134,344
Unrealized losses
Less than 12 months	1,397	1,154
12 months or longer	473	969
Total	$ 1,870	$ 2,123
No. of holdings | holding	436	370
Corporate debt securities
Fair value
Less than 12 months	$ 80,035	$ 39,693
12 months or longer	8,703	7,952
Total	88,738	47,645
Unrealized losses
Less than 12 months	584	644
12 months or longer	368	870
Total	$ 952	$ 1,514
No. of holdings | holding	289	257
Collateralized debt obligations
Fair value
Less than 12 months	$ 45,288	$ 50,036
12 months or longer	16,642	10,899
Total	61,930	60,935
Unrealized losses
Less than 12 months	148	232
12 months or longer	71	99
Total	$ 219	$ 331
No. of holdings | holding	73	65
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 9,240	$ 16,582
12 months or longer	476	0
Total	9,716	16,582
Unrealized losses
Less than 12 months	329	235
12 months or longer	34	0
Total	$ 363	$ 235
No. of holdings | holding	21	31
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 29,064	$ 8,163
12 months or longer	0	0
Total	29,064	8,163
Unrealized losses
Less than 12 months	301	34
12 months or longer	0	0
Total	$ 301	$ 34
No. of holdings | holding	46	13
Other debt securities
Fair value
Less than 12 months	$ 5,606	$ 1,019
12 months or longer	0	0
Total	5,606	1,019
Unrealized losses
Less than 12 months	35	9
12 months or longer	0	0
Total	$ 35	$ 9
No. of holdings | holding	7	4