Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2020 USD ($) Holdings	Dec. 31, 2019 USD ($) Holdings
Investment grade
Fair value
Less than 12 months	$ 135,419	$ 76,315
12 months or longer	13,721	46,390
Total	149,140	122,705
Unrealized losses
Less than 12 months	3,849	287
12 months or longer	526	218
Total	$ 4,375	$ 505
No. of holdings | Holdings	170	100
Non-investment grade
Fair value
Less than 12 months	$ 56,920	$ 11,421
12 months or longer	8,058	10,691
Total	64,978	22,112
Unrealized losses
Less than 12 months	3,881	324
12 months or longer	1,893	1,359
Total	$ 5,774	$ 1,683
No. of holdings | Holdings	473	146
Available-for-sale securities
Fair value
Less than 12 months	$ 192,339	$ 87,736
12 months or longer	21,779	57,081
Total	214,118	144,817
Unrealized losses
Less than 12 months	7,730	611
12 months or longer	2,419	1,577
Total	$ 10,149	$ 2,188
No. of holdings | Holdings	643	246
Corporate debt securities
Fair value
Less than 12 months	$ 81,468	$ 25,804
12 months or longer	8,058	15,699
Total	89,526	41,503
Unrealized losses
Less than 12 months	4,358	342
12 months or longer	1,893	1,362
Total	$ 6,251	$ 1,704
No. of holdings | Holdings	494	158
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 1,407	$ 16,712
12 months or longer	0	0
Total	1,407	16,712
Unrealized losses
Less than 12 months	2	50
12 months or longer	0	0
Total	$ 2	$ 50
No. of holdings | Holdings	3	7
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 30,808	$ 21,981
12 months or longer	0	372
Total	30,808	22,353
Unrealized losses
Less than 12 months	1,251	147
12 months or longer	0	1
Total	$ 1,251	$ 148
No. of holdings | Holdings	47	30
Collateralized debt obligations
Fair value
Less than 12 months	$ 75,876	$ 20,889
12 months or longer	13,721	41,010
Total	89,597	61,899
Unrealized losses
Less than 12 months	2,070	33
12 months or longer	526	214
Total	$ 2,596	$ 247
No. of holdings | Holdings	92	49
Other debt securities
Fair value
Less than 12 months	$ 2,780	$ 2,350
12 months or longer	0	0
Total	2,780	2,350
Unrealized losses
Less than 12 months	49	39
12 months or longer	0	0
Total	$ 49	$ 39
No. of holdings | Holdings	7	2