Quarterly report pursuant to Section 13 or 15(d)

CRUDE OIL AND NATURAL GAS PROPERTIES (Details)

v3.4.0.3
CRUDE OIL AND NATURAL GAS PROPERTIES (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2016
USD ($)
a
$ / a
Mar. 31, 2015
USD ($)
a
$ / a
Dec. 31, 2015
USD ($)
a
Acquisitions [Abstract]      
Capital expenditures incurred but not yet paid | $ $ 56.8   $ 59.5
Mineral acres acquired, net (in acres) | a 764 899  
Average acquisition cost per net acre (in dollars per acre) | $ / a 1,214 1,363  
Unproved Properties [Abstract]      
Unproven leasehold interests (in acres) | a 36,973   38,003
Anticipated future period over which excluded costs will become subject to depletion (in years) 5 years    
Impairment costs related to expired leases subject to depletion | $ $ 5.8 $ 23.6