Income Taxes - Pre-tax Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic operations	$ (12,852)	$ 165	$ (6,857)
Foreign operations	20,140	25,023	42,832
Income before provision for income taxes	$ 7,288	$ 25,188	$ 35,975