Significant Accounting Policies Foreign Currency (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Component of Other Operating Cost [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	$ 916	$ 1,832	$ 4,507
Foreign Currency Gain (Loss) [Member]
Component of Other Operating Cost [Line Items]
Other Nonoperating Income (Expense)	$ 916	$ 1,832	$ 4,507