Debt Narratives (Details) - USD ($) $ in Thousands	3 Months Ended					6 Months Ended	9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 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		63.00%					63.00%		76.00%
Interest Paid							$ 98,800	$ 99,300
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		$ 33,000					33,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Line of Credit Facility, Remaining Borrowing Capacity		$ 342,000					342,000
Line of Credit Facility, Increase (Decrease), Net		75,000		$ 30,000		$ 50,000
Repayments of Debt							902,700
Repayments of Long-term Debt							27,632	145,171
Gain (Loss) on Extinguishment of Debt		(25)			$ (6,918)		(22,503)	(6,918)
Repayments of Long-term Capital Lease Obligations							25,220	20,421
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					$ 90,000		10,000
Repayments of Debt								45,000
Repayments of Other Debt								342,500
Revolving Credit Facility
Debt Instrument [Line Items]
Repayments of Debt								100,000
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		325,000					325,000		0
Letters of Credit Outstanding, Amount		325,000					325,000
Repayments of Debt							17,500
March 2021 | Subsequent Event [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase (Decrease), Net	$ 170,000
April 2016 [Member]
Debt Instrument [Line Items]
Repayments of Debt								$ 197,400
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