Fair Value of Financial Instruments - Rollforward of Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financial Assets
Beginning balance	$ 357,195	$ 266,033	$ 295,178	$ 248,489
Transfers into Level 3	88,935	2,872	193,994	27,880
Transfers out of Level 3	(53,521)	(4,876)	(66,490)	(4,876)
Total gains or losses
Net investment gains (losses) included in net income related to financial assets	32	0	8	0
Net unrealized investment gains (losses) included in OCI	12,407	4,231	(20,462)	6,972
Purchases	0	1,566	8,765	1,566
Issuances	0	0	0	0
Sales	0	(607)	0	(607)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(5,324)	(14,506)	(11,269)	(24,711)
Ending balance	399,724	254,713	399,724	254,713
Financial Liabilities
Beginning balance	87,506	84,629	93,733	78,700
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	5,966	371	924	4,705
Net unrealized investment gains (losses) included in OCI	0	0	0	0
Purchases	0	0	0	0
Issuances	2,513	2,431	3,867	5,449
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(2,366)	(1,470)	(4,905)	(2,893)
Ending balance	93,619	85,961	93,619	85,961
Municipal bonds
Financial Assets
Beginning balance	104,892	47,756	44,291	47,531
Transfers into Level 3	10,726	0	74,477	0
Transfers out of Level 3	(45,917)	0	(45,917)	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	3,838	(537)	812	(193)
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(368)	(235)	(492)	(354)
Ending balance	73,171	46,984	73,171	46,984
Corporate bonds
Financial Assets
Beginning balance	111,693	82,482	103,952	80,742
Transfers into Level 3	13,970	2,808	32,803	5,882
Transfers out of Level 3	(4,166)	(4,876)	(14,188)	(4,876)
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	5,308	1,961	(173)	4,510
Purchases	0	1,566	6,875	1,566
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	(513)	(4,719)	(2,977)	(8,602)
Ending balance	126,292	79,222	126,292	79,222
Mortgage-Backed Securities
Financial Assets
Beginning balance	140,527	135,790	146,828	120,211
Transfers into Level 3	64,239	0	86,714	21,934
Transfers out of Level 3	(3,438)	0	(6,385)	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	3,261	2,807	(21,101)	2,655
Purchases	0	0	1,890	0
Issuances	0	0	0	0
Sales	0	(607)	0	(607)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(4,443)	(9,552)	(7,800)	(15,755)
Ending balance	200,146	128,438	200,146	128,438
Total Fixed Maturity Securities
Financial Assets
Beginning balance	357,112	266,028	295,071	248,484
Transfers into Level 3	88,935	2,808	193,994	27,816
Transfers out of Level 3	(53,521)	(4,876)	(66,490)	(4,876)
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	12,407	4,231	(20,462)	6,972
Purchases	0	1,566	8,765	1,566
Issuances	0	0	0	0
Sales	0	(607)	0	(607)
Settlements	0	0	0	0
Paydowns, maturities and distributions	(5,324)	(14,506)	(11,269)	(24,711)
Ending balance	399,609	254,644	399,609	254,644
Equity securities
Financial Assets
Beginning balance	83	5	107	5
Transfers into Level 3	0	64	0	64
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	32	0	8	0
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	0
Settlements	0	0	0	0
Paydowns, maturities and distributions	0	0	0	0
Ending balance	$ 115	$ 69	$ 115	$ 69

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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