Derivative Instruments - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	May 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Feb. 29, 2012
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative assets		164,878,000	$ 5,382,000
7.25% Senior Notes due 2019
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Debt hedged by interest rate derivatives	0.00%			33.33%
Annual interest rate		7.25%		7.25%
Cash proceeds from termination of interest rate swap	1,200,000
Commodity contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative assets		164,900,000
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