Fair Value of Financial Instruments - Rollforward of Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financial Assets
Beginning balance	$ 254,713	$ 271,651	$ 248,489	$ 230,257
Transfers into Level 3	39,921	17,030	67,801	90,661
Transfers out of Level 3	(3,271)	(970)	(8,147)	(16,479)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	46	0	46	(243)
Net unrealized investment gains (losses) included in OCI	2,983	(6,527)	9,955	(6,637)
Purchases	0	0	1,566	0
Issuances	0	0	0	0
Sales	0	(187)	(607)	(190)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(3,193)	(19,513)	(27,904)	(35,885)
Ending balance	291,199	261,484	291,199	261,484
Financial Liabilities
Beginning balance	85,961	77,788	78,700	80,733
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Total gains or losses
Net realized (gains) losses included in net income related to financial liabilities	3,661	2,205	8,366	(1,308)
Net unrealized investment gains (losses) included in OCI	0	0	0	0
Purchases	0	0	0	0
Issuances	2,033	3,940	7,482	7,379
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(2,557)	(1,668)	(5,450)	(4,539)
Ending balance	89,098	82,265	89,098	82,265
Total Fixed Maturity Securities
Financial Assets
Beginning balance	254,644	271,645	248,484	230,251
Transfers into Level 3	39,920	17,030	67,736	90,661
Transfers out of Level 3	(3,271)	(970)	(8,147)	(16,479)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0	0	(246)
Net unrealized investment gains (losses) included in OCI	2,983	(6,527)	9,955	(6,637)
Purchases	0	0	1,566	0
Issuances	0	0	0	0
Sales	0	(187)	(607)	(187)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(3,193)	(19,513)	(27,904)	(35,885)
Ending balance	291,083	261,478	291,083	261,478
Municipal bonds
Financial Assets
Beginning balance	46,984	49,921	47,531	49,328
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0	0	0
Net unrealized investment gains (losses) included in OCI	842	(471)	649	369
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(121)	(121)	(475)	(368)
Ending balance	47,705	49,329	47,705	49,329
Corporate bonds
Financial Assets
Beginning balance	79,222	92,663	80,742	72,979
Transfers into Level 3	18,916	0	24,798	40,487
Transfers out of Level 3	(2,822)	0	(7,698)	(11,279)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0	0	(246)
Net unrealized investment gains (losses) included in OCI	1,744	128	6,254	(1,459)
Purchases	0	0	1,566	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(387)	(3,926)	(8,989)	(11,617)
Ending balance	96,673	88,865	96,673	88,865
Mortgage-Backed Securities
Financial Assets
Beginning balance	128,438	129,061	120,211	107,944
Transfers into Level 3	21,004	17,030	42,938	50,174
Transfers out of Level 3	(449)	(970)	(449)	(5,200)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	0	0	0	0
Net unrealized investment gains (losses) included in OCI	397	(6,184)	3,052	(5,547)
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	(187)	(607)	(187)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(2,685)	(15,466)	(18,440)	(23,900)
Ending balance	146,705	123,284	146,705	123,284
Equity securities
Financial Assets
Beginning balance	69	6	5	6
Transfers into Level 3	1	0	65	0
Transfers out of Level 3	0	0	0	0
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	46	0	46	3
Net unrealized investment gains (losses) included in OCI	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	(3)
Settlements	0	0	0	0
Paydowns, maturities and distributions	0	0	0	0
Ending balance	$ 116	$ 6	$ 116	$ 6