XML 69 R51.htm IDEA: XBRL DOCUMENT v3.3.1.900
Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Assets:    
Total assets $ 156,215 $ 316,249
Money market funds    
Assets:    
Total assets 742 742
Commodity derivative instruments    
Assets:    
Total assets 155,473 315,507
Level 1    
Assets:    
Total assets 742 742
Level 1 | Money market funds    
Assets:    
Total assets 742 742
Level 1 | Commodity derivative instruments    
Assets:    
Total assets 0 0
Level 2    
Assets:    
Total assets 155,473 315,507
Level 2 | Money market funds    
Assets:    
Total assets 0 0
Level 2 | Commodity derivative instruments    
Assets:    
Total assets 155,473 315,507
Level 3    
Assets:    
Total assets 0 0
Level 3 | Money market funds    
Assets:    
Total assets 0 0
Level 3 | Commodity derivative instruments    
Assets:    
Total assets $ 0 $ 0