Summary of Significant Accounting Policies - Foreign Currencies (Details 8) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Nonoperating Income (Expense) [Member]
Foreign Currencies
Foreign currency (loss) gain	$ 3,052	$ (3,714)	$ (6,299)