Summary of Significant Accounting Policies (Revenue Recognition) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Remaining Performance Obligation, Amount		$ 806,900	$ 851,800
Revenues		$ 761,608	$ 735,994	$ 724,944
Decrease to operating income from the quarterly impact of revisions in long term contracts				$ 5,700
Inventory Write-down	$ 32,500
Percentage of pre-contract inventory (less than)		1.00%	1.00%
Performance obligations satisfied in previous periods [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ (4,600)	$ 6,700