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