Revenues - Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Contract assets	$ 62,467	$ 75,371
Contract liabilities	(32,339)	(51,597)	$ (62,700)
Net contract assets	30,128	23,774
Contract assets, held-for-sale	1,800	1,300
Contract liabilities, held-for-sale	100	$ 5,500
Difference Between Work Performed On Open Contracts And Contractual Billing Terms
Revenue from External Customer [Line Items]
Changes in contract assets, decrease	(12,900)
Difference Related To Customer Advances On Certain Contract
Revenue from External Customer [Line Items]
Changes in contract assets, decrease	$ (19,300)