XML 109 R51.htm IDEA: XBRL DOCUMENT

Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Total assets	$ 316,249us-gaap_AssetsFairValueDisclosure	$ 4,339us-gaap_AssetsFairValueDisclosure
Liabilities:
Total liabilities		8,327us-gaap_LiabilitiesFairValueDisclosure
Money market funds [Member]
Assets:
Total assets	742	742
Commodity derivative instruments [Member]
Assets:
Total assets	315,507	3,597
Liabilities:
Total liabilities		8,327
Level 1 [Member] \| Money market funds [Member]
Assets:
Total assets	742	742
Level 2 [Member]
Assets:
Total assets		3,597
Liabilities:
Total liabilities		8,327
Level 2 [Member] \| Commodity derivative instruments [Member]
Assets:
Total assets	315,507	3,597
Liabilities:
Total liabilities		$ 8,327