Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating revenues	$ 1,296,210	$ 1,102,465	$ 2,549,174	$ 2,193,982
Provision for bad debts		(36)	102	745
Changes in accounts receivable			(5,774)	(140,949)
Accounts receivable					$ 691,732
Allowance for doubtful accounts					0
Accounts receivable	$ 775,610		$ 775,610		691,732
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating revenues		1,120,675		2,232,036
Provision for bad debts		18,174		38,799
Changes in accounts receivable				(179,003)
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		(18,210)		(38,054)
Provision for bad debts		$ (18,210)		(38,054)
Changes in accounts receivable				$ 38,054
Accounts receivable					(75,544)
Allowance for doubtful accounts					(75,544)
Accounts receivable					$ 0