Long-Term Debt Revolving Credit Facility (Details) - USD ($) $ in Thousands		Oct. 26, 2017	Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Credit facility balance			$ 0	$ 0
Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, maximum loan amount			2,500,000
Line of credit agreement, aggregate lender commitment amount			925,000	1,165,000
Credit facility balance	[1]		0	0
Letters of credit outstanding, amount	[2]		200	200
Available borrowing capacity			924,800	1,164,800
Unamortized deferred financing costs			$ 3,500	$ 5,900
Subsequent Event [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, aggregate lender commitment amount		$ 925,000
Credit facility balance	[1]	0
Letters of credit outstanding, amount	[2]	200
Available borrowing capacity		$ 924,800

[1] Unamortized deferred financing costs attributable to the credit facility are presented as a component of other noncurrent assets on the accompanying balance sheets and totaled $3.5 million and $5.9 million as of September 30, 2017, and December 31, 2016, respectively.

[2] Letters of credit outstanding reduce the amount available under the credit facility on a dollar-for-dollar basis.