Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Pre-Tax Amount
December 31, 2017	$ 12,044
Pretax Cumulative Effect of New Accounting Principal in Period of Adoption		$ (12,300)
Changes in net unrealized gains on investments	(11,084)
AOCI Before Tax Attributable to Parent after Cumulative Effect Adjustment		(256)
Reclassification adjustment for realized gains	(211)
March 31, 2018	(11,551)
Tax (Expense) Benefit
December 31, 2017	(2,823)
Tax Cumulative Effect of New Accounting Principal in Period of Adoption		2,962
AOCI Tax Attributable to Parent After Cumulative Effect Adjustment		139
Changes in net unrealized gains on investments	2,908
Reclassification adjustment for realized gains	53
March 31, 2018	3,100
Net-of-Tax Amount
December 31, 2017	9,221
Cumulative Effect of New Accounting Principle in Period of Adoption		(9,338)
AOCI Net of Tax After Cumulative Effect Adjustment		$ (117)
Changes in net unrealized gains on investments	(8,176)
Reclassification adjustment for realized gains	158
March 31, 2018	$ (8,451)