Income Taxes - Income (Loss) From Continuing Operations Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
US operations	$ 37,850	$ (22,220)	$ 26,852
Foreign operations	5,502	(1,339)	(1,154)
Income (loss) before provision for income taxes	$ 43,352	$ (23,559)	$ 25,698