Income Taxes - Unrecognized Tax Benefits (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]
Balance	$ 6,018	$ 8,083	$ 8,022
Additions related to current year tax positions	708	193	61
Reductions for prior year tax positions	(2,843)
Balance	$ 3,883	$ 6,018	$ 8,083