Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Derivative Asset, Current	$ 2,672	$ 0
Derivative Asset, Noncurrent	584	0
Liabilities:
Commodity derivative liabilities – current	0	12,932
Derivative Liability, Noncurrent	90	14,437
Fair Value, Measurements, Recurring | Commodity contracts
Assets:
Derivative Asset, Current	2,672
Derivative Asset, Noncurrent	584
Liabilities:
Commodity derivative liabilities – current	0	12,932
Derivative Liability, Noncurrent	90	14,437
Fair Value, Measurements, Recurring | Commodity contracts | Level 1
Assets:
Derivative Asset, Current	0
Derivative Asset, Noncurrent	0
Liabilities:
Commodity derivative liabilities – current	0	0
Derivative Liability, Noncurrent	0	0
Fair Value, Measurements, Recurring | Commodity contracts | Level 2
Assets:
Derivative Asset, Current	2,672
Derivative Asset, Noncurrent	584
Liabilities:
Commodity derivative liabilities – current	0	12,932
Derivative Liability, Noncurrent	90	14,437
Fair Value, Measurements, Recurring | Commodity contracts | Level 3
Assets:
Derivative Asset, Current	0
Derivative Asset, Noncurrent	0
Liabilities:
Commodity derivative liabilities – current	0	0
Derivative Liability, Noncurrent	$ 0	$ 0