Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income and (Loss), Pre-Tax Amount, Beginning of period	$ 1,464	$ 2,640	$ 6,537
Change in net unrealized gain (loss) on investments, Pre-Tax Amount	10,647	(629)	(3,070)
Reclassification adjustment for realized gains, Pre-Tax Amount	(67)	(547)	(827)
Accumulated Other Comprehensive Income and (Loss), Pre-Tax Amount, End of period	12,044	1,464	2,640
Accumulated Other Comprehensive Income (Loss), Tax (Expense) Benefit, Beginning of period	642	1,020	2,526
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(3,747)	167	1,187
Reclassification adjustment for realized losses, Tax (Expense) Benefit	17	211	319
Accumulated Other Comprehensive Income (Loss), Tax (Expense) Benefit, End of period	2,823	642	1,020
Accumulated Other Comprehensive Income (Loss), Net-of-Tax Amount, Beginning of period	822	1,620	4,011
Change in net unrealized gain (loss) on investments, Net-of-Tax Amount		(462)	(1,883)
Reclassification adjustment for realized gains, Net-of-Tax Amount	(50)	(336)	(508)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	6,900
Accumulated Other Comprehensive Income (Loss), Net-of-Tax Amount, End of period	9,221	$ 822	$ 1,620
Cumulative Effect of New Accounting Principle in Period of Adoption	1,549
Cumulative Effect of New Accounting Principle in Period of Adoption, Tax Benefit	$ 1,549