Summary of Significant Accounting Policies (Revenue Recognition) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 631,200	$ 806,900
Revenues	784,459	761,608	$ 735,994
Inventory Write-down			32,500
Inventory Write-down			32,500
Performance obligations satisfied in previous periods [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to operating income from the quarterly impact of revisions in long term contracts			$ 6,700
Reductions in revenue	$ (7,000)	$ (4,600)