Income Taxes - Income Tax Uncertainties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning	$ 1,115	$ 788	$ 278
Additions for prior year tax positions	50	454	625
Additions for current year tax positions	29	0	0
Reductions for tax positions of prior years	0	(25)	(8)
Lapse of statute of limitations	(67)	(102)	(25)
Settlements	0	0	(82)
Unrecognized tax benefits, ending	$ 1,127	$ 1,115	$ 788