Derivative Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative assets	150,253	$ 164,878
Commodity contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative assets	150,300
Number of derivative counterparties	7
Commodity contracts | Credit Concentration Risk
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Number of derivative counterparties	5
Commodity contracts | Natural Gas
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Third-party quoted forward prices	NYMEX Henry Hub gas
Commodity contracts | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Third-party quoted forward prices	West Texas Intermediate crude oil