Revenue - Contract Balances (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Contract with Customer, Asset, Net, Current [Abstract]
Contract with Customer, Receivable, Net, Current	$ 184,993
Contract with Customer, Receivable, Current, Net Increase (Decrease)	38,113
Contract with Customer, Receivable, Net, Current	223,106
Contract with Customer, Asset, Net, Noncurrent [Abstract]
Contract with Customer, Receivable, Net, Noncurrent	34,008
Contract with Customer, Receivable, NonCurrent, Net Increase (Decrease)	7,011
Contract with Customer, Receivable, Net, Noncurrent	41,019
Contract with Customer, Liability, Current [Abstract]
Contract with Customer, Liability, Current	3,147
Contract with Customer, Liability, Current, Net Increase (Decrease)	2,113
Contract with Customer, Liability, Current	5,260
Contract with Customer, Liability, Noncurrent [Abstract]
Contract with Customer, Liability, Noncurrent	1,834
Contract with Customer, Liability, Noncurrent, Net Increase (Decrease)	(103)
Contract with Customer, Liability, Noncurrent	$ 1,731