Quarterly report pursuant to Section 13 or 15(d)

Acquisitions and Divestitures - Business Acquisition Pro Forma Information Incremental Items (Parenthetical) (Details)

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Acquisitions and Divestitures - Business Acquisition Pro Forma Information Incremental Items (Parenthetical) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Business Acquisition [Line Items]        
Long-term debt, less current maturities   $ 1,468,870   $ 1,360,057
Federal statutory income tax rate   35.00%    
Woodside Properties        
Business Acquisition [Line Items]        
Long-term debt, less current maturities $ 55,000   $ 55,000  
Effective interest rate 1.80%   1.80%  
Federal statutory income tax rate 35.00%   35.00%