Debt (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Repayments of Debt				$ 893,800
Letters of Credit Outstanding, Amount	$ 33,300			33,300
Line of Credit Facility, Increase (Decrease), Net	50,000	$ 30,000
Bank Credit Facility	0			0		$ 270,000
Unamortized debt issuance costs	(35,686)			(35,686)		(42,491)
Total debt	3,203,283			3,203,283		3,124,428
Less: Current maturities of long-term debt	(90,104)			(90,104)		(86,823)
Total long-term debt	3,113,179			3,113,179		3,037,605
July 2018
Debt Instrument [Line Items]
Repayments of Other Debt					$ 30,100
Line of Credit Facility, Increase (Decrease), Net			$ 30,000	10,000
March 2021
Debt Instrument [Line Items]
Term Loan	691,250			691,250		0
Letters of Credit Outstanding, Amount	250,000			250,000
Bank Credit Facility	250,000			250,000		0
Unsecured Debt
Debt Instrument [Line Items]
Unamortized pricing discounts and other	8,730			8,730		8,636
Unsecured Debt | June 2017
Debt Instrument [Line Items]
Senior Notes	0			0
Repayments of Debt		$ 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	210,037			210,037		204,246
Mortgages [Member]
Debt Instrument [Line Items]
Mortgage notes and other debt	$ 3,952			$ 3,952		$ 4,037