Income Taxes - Unrecognized Tax Benefit Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 1,185	$ 400	$ 702
Decrease attributable to settlements			(174)
Increase attributable to tax positions taken during a prior period		925	12
Decrease attributable to lapse of statute of limitations	(365)	(140)	(140)
Unrecognized tax benefits, ending balance	$ 820	$ 1,185	$ 400