Debt Narratives (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate		4.60%			4.60%		5.20%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate		65.00%			65.00%		76.00%
Interest Paid					$ 80,200	$ 81,100
Bank Credit Agreement		$ 1,400,000			1,400,000
Letters of Credit, Maximum Borrowing Capacity		100,000			100,000		$ 175,000
Line of Credit Facility, Amount Outstanding		0			0		270,000
Letters of Credit Outstanding, Amount		$ 33,300			33,300
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Line of Credit Facility, Remaining Borrowing Capacity		$ 416,700			416,700
Line of Credit Facility, Increase (Decrease), Net		50,000	$ 30,000
Repayments of Debt					893,800
Repayments of Long-term Debt					18,835	30,121
Gain (Loss) on Extinguishment of Debt		(21,898)		$ 0	(22,479)	0
Capital Lease Obligations Incurred					23,400	22,500
Repayments of Long-term Capital Lease Obligations					16,907	15,257
Debt Issuance Costs, Line of Credit Arrangements, Net		5,200			5,200
Term Loan Increase Decrease For Period			$ 550,000
Subsequent Event [Member]
Debt Instrument [Line Items]
Term Loan Increase Decrease For Period	$ 150,000
July 2018
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							500,000
Term Loan, Maximum Borrowing Capacity							600,000
Line of Credit Facility, Increase (Decrease), Net				$ 30,000	10,000
Repayments of Other Debt						$ 30,100
March 2021
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		700,000			700,000
Term Loan, Maximum Borrowing Capacity		700,000			700,000
Line of Credit Facility, Amount Outstanding		250,000			250,000		0
Letters of Credit Outstanding, Amount		250,000			250,000
March 2021 | Subsequent Event [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net	$ 170,000
Unsecured Debt | May 2024
Debt Instrument [Line Items]
Senior Notes		$ 850,000			850,000		$ 850,000
Unsecured Debt | July 2018
Debt Instrument [Line Items]
Repayments of Debt					310,000
Unsecured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Repayments of Debt					$ 280,000