Fair Value of Financial Instruments - Transfers Between Different Fair Value Levels (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Financial Assets
Beginning balance	$ 248,489	$ 230,257
Transfers into Level 3	90,306	91,259
Transfers out of Level 3	(10,266)	(16,479)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(1,067)	(484)
Net unrealized investment gains (losses) included in OCI	11,035	(9,605)
Purchases	2,483	0
Issuances	0	0
Sales	(608)	(6,326)
Settlements	0	0
Paydowns, maturities and distributions	(45,194)	(40,133)
Ending balance	295,178	248,489
Financial Liabilities
Beginning balance	78,700	80,733
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains or losses
Net realized (gains) losses included in net income related to financial liabilities	12,636	(7,518)
Net unrealized investment gains (losses) included in OCI	0	0
Purchases	0	0
Issuances	10,039	11,183
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(7,642)	(5,698)
Ending balance	93,733	78,700
Municipal bonds
Financial Assets
Beginning balance	47,531	49,328
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 assets	0	0
Net unrealized investment gains (losses) included in OCI	474	(1,195)
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(3,714)	(602)
Ending balance	44,291	47,531
Corporate bonds
Financial Assets
Beginning balance	80,742	72,979
Transfers into Level 3	33,475	40,488
Transfers out of Level 3	(7,698)	(11,279)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	(487)
Net unrealized investment gains (losses) included in OCI	4,461	(2,840)
Purchases	2,483	0
Issuances	0	0
Sales	0	(6,135)
Settlements	0	0
Paydowns, maturities and distributions	(9,511)	(11,984)
Ending balance	103,952	80,742
Other mortgage-backed securities
Financial Assets
Beginning balance	120,211	107,944
Transfers into Level 3	56,766	50,771
Transfers out of Level 3	(2,568)	(5,200)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(1,105)	0
Net unrealized investment gains (losses) included in OCI	6,100	(5,570)
Purchases	0	0
Issuances	0	0
Sales	(607)	(187)
Settlements	0	0
Paydowns, maturities and distributions	(31,969)	(27,547)
Ending balance	146,828	120,211
Total
Financial Assets
Beginning balance	248,484	230,251
Transfers into Level 3	90,241	91,259
Transfers out of Level 3	(10,266)	(16,479)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	(1,105)	(487)
Net unrealized investment gains (losses) included in OCI	11,035	(9,605)
Purchases	2,483	0
Issuances	0	0
Sales	(607)	(6,322)
Settlements	0	0
Paydowns, maturities and distributions	(45,194)	(40,133)
Ending balance	295,071	248,484
Equity securities
Financial Assets
Beginning balance	5	6
Transfers into Level 3	65	0
Transfers out of Level 3	0	0
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	38	3
Net unrealized investment gains (losses) included in OCI	0	0
Purchases	0	0
Issuances	0	0
Sales	(1)	(4)
Settlements	0	0
Paydowns, maturities and distributions	0	0
Ending balance	$ 107	$ 5

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