Debt (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Repayments of Debt					$ 902,700
Letters of Credit Outstanding, Amount	$ 33,000				33,000
Line of Credit Facility, Increase (Decrease), Net	75,000	$ 30,000		$ 50,000
Bank Credit Facility	0				0		$ 270,000
Unamortized debt issuance costs	(34,343)				(34,343)		(42,491)
Total debt	3,271,225				3,271,225		3,124,428
Less: Current maturities of long-term debt	(89,531)				(89,531)		(86,823)
Total long-term debt	3,181,694				3,181,694		3,037,605
July 2018
Debt Instrument [Line Items]
Repayments of Other Debt						$ 342,500
Repayments of Debt						$ 45,000
Line of Credit Facility, Increase (Decrease), Net			$ 90,000		10,000
March 2021
Debt Instrument [Line Items]
Repayments of Debt					17,500
Term Loan	682,500				682,500		0
Letters of Credit Outstanding, Amount	325,000				325,000
Bank Credit Facility	325,000				325,000		0
Unsecured Debt
Debt Instrument [Line Items]
Unamortized pricing discounts and other	8,522				8,522		8,636
Unsecured Debt | June 2017
Debt Instrument [Line Items]
Senior Notes	0				0		295,000
Unsecured Debt | October 2018
Debt Instrument [Line Items]
Senior Notes	250,000				250,000		250,000
Unsecured Debt | November 2020
Debt Instrument [Line Items]
Senior Notes	200,000				200,000		200,000
Unsecured Debt | November 2021
Debt Instrument [Line Items]
Senior Notes	150,000				150,000		150,000
Unsecured Debt | January 2022
Debt Instrument [Line Items]
Senior Notes	425,000				425,000		425,000
Unsecured Debt | May 2024
Debt Instrument [Line Items]
Senior Notes	850,000				850,000		850,000
Unsecured Debt | April 2027
Debt Instrument [Line Items]
Senior Notes	200,000				200,000		200,000
Unsecured Debt | July 2018
Debt Instrument [Line Items]
Repayments of Debt					310,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Term Loan	0				0		310,000
Line of Credit [Member]
Debt Instrument [Line Items]
Bank Credit Facility	0				0		270,000
Capital Lease Obligations
Debt Instrument [Line Items]
Obligations under capital leases	210,760				210,760		204,246
Mortgages [Member]
Debt Instrument [Line Items]
Mortgage notes and other debt	$ 3,786				$ 3,786		$ 4,037