Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating revenues	$ 1,252,964	$ 1,091,517
Provision for bad debts	85	781
Changes in accounts receivable	(45,811)	(118,269)
Accounts receivable			$ 691,732
Allowance for doubtful accounts			0
Accounts receivable	$ 806,391		691,732
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating revenues		1,111,361
Provision for bad debts		20,625
Changes in accounts receivable		(138,113)
Accounts receivable			767,276
Allowance for doubtful accounts			75,544
Accounts receivable			691,732
Accounting Standards Update 2014-09 | Adoption Impact
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating revenues		(19,844)
Provision for bad debts		(19,844)
Changes in accounts receivable		$ 19,844
Accounts receivable			(75,544)
Allowance for doubtful accounts			(75,544)
Accounts receivable			$ 0