Fair Value of Financial Instruments - Transfers Between Different Fair Value Levels (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Financial Assets
Beginning balance	$ 295,178	$ 248,489
Transfers into Level 3	268,804	90,306
Transfers out of Level 3	(190,373)	(10,266)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(277)	(1,067)
Net unrealized investment gains (losses) included in OCI	(4,792)	11,035
Purchases	8,765	2,483
Issuances	0	0
Sales	1,214	(608)
Settlements	0	0
Paydowns, maturities and distributions	(23,453)	(45,194)
Ending balance	355,066	295,178
Financial Liabilities
Beginning balance	93,733	78,700
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains or losses
Net investment (gains) losses included in net income related to financial liabilities	11,499	12,636
Net unrealized investment gains (losses) included in OCI	0	0
Purchases	0	0
Issuances	8,373	10,039
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(9,117)	(7,642)
Ending balance	104,488	93,733
Municipal bonds
Financial Assets
Beginning balance	44,291	47,531
Transfers into Level 3	80,686	0
Transfers out of Level 3	(69,074)	0
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in OCI	4,252	474
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(565)	(3,714)
Ending balance	59,590	44,291
Corporate bonds
Financial Assets
Beginning balance	103,952	80,742
Transfers into Level 3	83,621	33,475
Transfers out of Level 3	(36,620)	(7,698)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in OCI	1,427	4,461
Purchases	6,875	2,483
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(3,439)	(9,511)
Ending balance	155,816	103,952
Other asset-backed securities
Financial Assets
Beginning balance	146,828	120,211
Transfers into Level 3	104,263	56,766
Transfers out of Level 3	(84,679)	(2,568)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(239)	(1,105)
Net unrealized investment gains (losses) included in OCI	(10,471)	6,100
Purchases	1,890	0
Issuances	0	0
Sales	1,214	(607)
Settlements	0	0
Paydowns, maturities and distributions	(19,449)	(31,969)
Ending balance	139,357	146,828
Total
Financial Assets
Beginning balance	295,071	248,484
Transfers into Level 3	268,570	90,241
Transfers out of Level 3	(190,373)	(10,266)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(239)	(1,105)
Net unrealized investment gains (losses) included in OCI	(4,792)	11,035
Purchases	8,765	2,483
Issuances	0	0
Sales	1,214	(607)
Settlements	0	0
Paydowns, maturities and distributions	(23,453)	(45,194)
Ending balance	354,763	295,071
Equity securities
Financial Assets
Beginning balance	107	5
Transfers into Level 3	234	65
Transfers out of Level 3	0	0
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(38)	38
Net unrealized investment gains (losses) included in OCI	0	0
Purchases	0	0
Issuances	0	0
Sales	0	(1)
Settlements	0	0
Paydowns, maturities and distributions	0	0
Ending balance	$ 303	$ 107

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