Supplemental Consolidated Balance Sheet and Statement of Operations Information Other Income (Expense), Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	$ (2,944)	$ 0	$ 0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	$ 200	$ 100