Summary of Significant Accounting Policies - Major Customers (Detail) (Customer Concentration Risk [Member], Revenues [Member])
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Significant Accounting Policies [Line Items]      
Total Reported Revenues 10.00%    
Phillips 66 [Member]
      
Significant Accounting Policies [Line Items]      
Total Reported Revenues 12.00% [1] 14.00% [1] 12.00% [1]
Conoco Phillips [Member]
      
Significant Accounting Policies [Line Items]      
Total Reported Revenues     13.00% [1]
Sinclair Oil & Gas Company [Member]
      
Significant Accounting Policies [Line Items]      
Total Reported Revenues 11.00%    
[1] Phillips 66 purchased production pursuant to existing marketing agreements with terms that are currently on “evergreen” status. Evergreen contracts automatically renew on a month-to-month basis until either party gives 30 or 60 days advance written notice of non-renewal. Phillips 66 was a subsidiary of ConocoPhillips through April 30, 2012. Accordingly, any revenues generated from Phillips 66 prior to May 1, 2012 were reported under ConocoPhillips.