Basis of Presentation and Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated translation losses	$ 8,800,000	$ 16,300,000
Foreign currency exchange gains (losses)	$ 8,000	$ 109,000	$ (1,650,000)