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Acquisition and Dispositions of Properties - Additional Information (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2016
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
MMBoe
Gas and Oil Acreage [Line Items]        
Payment for unproved leasehold $ 7.6   $ 85.7  
San Juan Basin        
Gas and Oil Acreage [Line Items]        
Amount of consideration received   $ 395.0    
Purchase price adjustments   11.0    
Pre-tax proceeds   384.0    
Transaction costs   2.8    
Proved developed reserves (MMBOE) | MMBoe       69.038
San Juan | San Juan Basin        
Gas and Oil Acreage [Line Items]        
Pre-tax gain on disposal   $ 27.0