Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2020 USD ($) holding	Dec. 31, 2019 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 86,807	$ 76,315
12 months or longer	10,899	46,390
Total	97,706	122,705
Unrealized losses
Less than 12 months	561	287
12 months or longer	99	218
Total	$ 660	$ 505
No. of holdings | holding	119	100
Non-investment grade
Fair value
Less than 12 months	$ 28,686	$ 11,421
12 months or longer	7,952	10,691
Total	36,638	22,112
Unrealized losses
Less than 12 months	593	324
12 months or longer	870	1,359
Total	$ 1,463	$ 1,683
No. of holdings | holding	251	146
Corporate debt securities
Fair value
Less than 12 months	$ 39,693	$ 25,804
12 months or longer	7,952	15,699
Total	47,645	41,503
Unrealized losses
Less than 12 months	644	342
12 months or longer	870	1,362
Total	$ 1,514	$ 1,704
No. of holdings | holding	257	158
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 8,163	$ 16,712
12 months or longer	0	0
Total	8,163	16,712
Unrealized losses
Less than 12 months	34	50
12 months or longer	0	0
Total	$ 34	$ 50
No. of holdings | holding	13	7
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 16,582	$ 21,981
12 months or longer	0	372
Total	16,582	22,353
Unrealized losses
Less than 12 months	235	147
12 months or longer	0	1
Total	$ 235	$ 148
No. of holdings | holding	31	30
Collateralized debt obligations
Fair value
Less than 12 months	$ 50,036	$ 20,889
12 months or longer	10,899	41,010
Total	60,935	61,899
Unrealized losses
Less than 12 months	232	33
12 months or longer	99	214
Total	$ 331	$ 247
No. of holdings | holding	65	49
Other debt securities
Fair value
Less than 12 months	$ 1,019	$ 2,350
12 months or longer	0	0
Total	1,019	2,350
Unrealized losses
Less than 12 months	9	39
12 months or longer	0	0
Total	$ 9	$ 39
No. of holdings | holding	4	2
Available-for-sale securities
Fair value
Less than 12 months	$ 115,493	$ 87,736
12 months or longer	18,851	57,081
Total	134,344	144,817
Unrealized losses
Less than 12 months	1,154	611
12 months or longer	969	1,577
Total	$ 2,123	$ 2,188
No. of holdings | holding	370	246