Inventories (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Inventory
Raw materials		$ 358,827	$ 348,012
Work in process		548,250	629,766
Finished goods		215,849	206,086
Less: Progress billings		(160,044)	(216,783)
Less: Excess and obsolete reserve		(78,609)	(69,391)
Inventories, net		884,273	897,690
Expenses due to excess and obsolete inventory	$ 16,900	$ 22,900	$ 14,600	$ 20,200