Revenue - Contract Balances (Details) $ in Thousands	6 Months Ended
	Jun. 30, 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)	89,004
Contract with Customer, Receivable, Net, Current	273,997
Contract with Customer, Asset, Net, Noncurrent [Abstract]
Contract with Customer, Receivable, Net, Noncurrent	34,008
Contract with Customer, Receivable, NonCurrent, Net Increase (Decrease)	17,610
Contract with Customer, Receivable, Net, Noncurrent	51,618
Contract with Customer, Liability, Current [Abstract]
Contract with Customer, Liability, Current	3,147
Contract with Customer, Liability, Current, Net Increase (Decrease)	3,234
Contract with Customer, Liability, Current	6,381
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