Income Taxes - Valuation Allowance (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Deferred tax asset, valuation allowance		$ 5,368	$ 140,915
Charged to income tax expense (benefit)		(103)	2,305
Foreign currency		(56)	313
Release valuation allowance	$ (141,100)	(3,969)	(141,094)
Deferred tax asset, valuation allowance	$ 5,368	$ 1,240	$ 5,368
ASU 2016-09
Valuation Allowance [Line Items]
Adoption of ASU 2016-09				$ 2,929