Inventory (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 201,429	$ 190,045
Work in process	374,505	302,042
Finished goods	22,848	21,791
Deferred costs	221,615	212,260
Total Inventories	$ 820,397	$ 726,138