Equity Method Investments - Summarized Financial Information of Equity Method Investments, Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Revenue	$ 700	$ 1,239	$ 10,866
Gross (loss) profit	(3,467)	(2,313)	7,628
Net (loss) income	$ (5,834)	$ (12,353)	$ 1,412