Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Additional Information (Detail)

v2.4.0.8
Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2013
MMcf
Dec. 31, 2013
MMcf
Dec. 31, 2012
Dec. 31, 2011
Significant Accounting Policies [Line Items]        
Increase in production 2,600 1,900    
Natural gas imbalances $ 6.4 $ 6.4 $ 6.0  
Percentage of discount from proved reserves   10.00%    
Ceiling test impairment   0 0 0
Payments received related to break-up fee and termination of certain purchase and sale agreement   9.2    
Third-party expenses related to the cancelled transaction   0.1    
Fixtures and Non-Oil and Natural Gas Property and Equipment | Minimum
        
Significant Accounting Policies [Line Items]        
Estimated useful lives   5 years    
Fixtures and Non-Oil and Natural Gas Property and Equipment | Maximum
        
Significant Accounting Policies [Line Items]        
Estimated useful lives   7 years    
Natural Gas
        
Significant Accounting Policies [Line Items]        
Adjustment to depreciation, depletion, amortization and accretion 7.1 5.0    
Reduction in net income $ 4.6 $ 3.2