Income Taxes - Valuation Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1	$ 13,179	$ 7,832	$ 2,006
Charged to costs and expenses	(1,114)	5,347	6,625
(Deductions)/Other	0	0	(799)
Balance at December 31	$ 12,065	$ 13,179	$ 7,832