Fair Value of Financial Instruments - Rollforward of Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Financial Assets
Beginning balance	$ 248,489	$ 230,257
Transfers into Level 3	25,008	25,600
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	3
Net unrealized investment gains (losses) included in other comprehensive income	2,741	(1,466)
Purchases	0	0
Issuances	0	0
Sales	0	(3)
Settlements	0	0
Paydowns, maturities and distributions	(10,205)	(10,523)
Ending balance	266,033	243,868
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	4,334	(2,222)
Net unrealized investment gains (losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	3,018	1,332
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(1,423)	(1,357)
Ending balance	84,629	78,486
Short-term Investments
Financial Assets
Beginning balance	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	0	0
Ending balance	0	0
Total Fixed Maturity Securities
Financial Assets
Beginning balance	248,484	230,251
Transfers into Level 3	25,008	25,600
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in other comprehensive income	2,741	(1,466)
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(10,205)	(10,523)
Ending balance	266,028	243,862
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 realized investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in other comprehensive income	344	443
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(119)	(23)
Ending balance	47,756	49,748
Corporate bonds
Financial Assets
Beginning balance	80,742	72,979
Transfers into Level 3	3,074	10,778
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in other comprehensive income	2,549	(887)
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(3,883)	(4,090)
Ending balance	82,482	78,780
Mortgage-Backed Securities
Financial Assets
Beginning balance	120,211	107,944
Transfers into Level 3	21,934	14,822
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	0
Net unrealized investment gains (losses) included in other comprehensive income	(152)	(1,022)
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Paydowns, maturities and distributions	(6,203)	(6,410)
Ending balance	135,790	115,334
Equity securities
Financial Assets
Beginning balance	5	6
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains or losses
Net realized investment gains (losses) included in net income related to financial assets	0	3
Net unrealized investment gains (losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	(3)
Settlements	0	0
Paydowns, maturities and distributions	0	0
Ending balance	$ 5	$ 6

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Amount of gain (loss) recognized in the income statement for 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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Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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