Revenue - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Contract with Customer, Asset, Net, Current [Roll Forward]
Contract with Customer, Receivable, Net, Current	$ 309,075	$ 184,993
Contract with Customer, Receivable, Current, Net Increase (Decrease)	7,803	89,004
Contract with Customer, Receivable, Net, Current	316,878	273,997
Contract with Customer, Asset, Gross, Current	2,833	0
Contract with Customer, Contract Asset, Current, Net Increase (Decrease)	72,701	0
Contract with Customer, Asset, Gross, Current	75,534	0
Contract with Customer, Asset, Net, Noncurrent [Roll Forward]
Contract with Customer, Receivable, Net, Noncurrent	60,948	34,008
Contract with Customer, Receivable, NonCurrent, Net Increase (Decrease)	1,700	17,610
Contract with Customer, Receivable, Net, Noncurrent	62,648	51,618
Contract with Customer, Asset, Gross, Noncurrent	541	0
Increase (Decrease) in Contract Receivables, Net	6,740	0
Contract with Customer, Asset, Gross, Noncurrent	7,281	0
Contract with Customer, Liability, Current [Roll Forward]
Contract with Customer, Liability, Current	4,016	3,147
Contract with Customer, Liability, Current, Net Increase (Decrease)	1,049	3,234
Contract with Customer, Liability, Current	5,065	6,381
Contract with Customer, Liability, Noncurrent [Roll Forward]
Contract with Customer, Liability, Noncurrent	1,731	1,834
Contract with Customer, Liability, Noncurrent, Net Increase (Decrease)	(812)	(103)
Contract with Customer, Liability, Noncurrent	$ 919	$ 1,731