Summary of Significant Accounting Policies Impact of New Accounting Pronouncements - Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Income (Loss) Attributable to Parent	$ 16,469	$ 8,171	$ 38,100	$ (9,427)
Increase (Decrease) in Other Accrued Liabilities			3,834
Increase (Decrease) in Deferred Revenue			185	6,061
Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable			(2,003)	(44)
Increase (Decrease) in Other Operating Assets and Liabilities, Net			(3,761)	$ (3,000)
Accounting Standards Update 2014-09 [Member]
Net Income (Loss) Attributable to Parent	16,499		37,820
Increase (Decrease) in Other Accrued Liabilities			(1,479)
Increase (Decrease) in Deferred Revenue			2,843
Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable			(2,123)
Increase (Decrease) in Other Operating Assets and Liabilities, Net			(705)
Accounting Standards Update 2014-09 [Member]
Net Income (Loss) Attributable to Parent	$ (30)		280
Increase (Decrease) in Other Accrued Liabilities			5,313
Increase (Decrease) in Deferred Revenue			(2,658)
Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable			120
Increase (Decrease) in Other Operating Assets and Liabilities, Net			$ (3,056)