Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Jun. 30, 2013	Dec. 31, 2013	Feb. 29, 2012
Revolving credit facility
Debt Disclosure [Line Items]
Maximum borrowing capacity	$ 450,000,000
Optional additional borrowing	150,000,000
Revolving credit facility, Borrowing base	500,000,000
Letter of credit amount outstanding	1,800,000
Available borrowing capacity	413,200,000
Credit facility interest rate option two, base rate over federal funds effective rate	0.50%
Debt Instrument, Description of Variable Rate Basis	one-month Adjusted LIBOR
Credit facility interest rate option two, base rate over one-month Adjusted LIBOR	1.00%
Credit facility interest rate option two, applicable margin rate	1.50%
Line of Credit Facility, Interest Rate at Period End	1.6875%
Line Of Credit Facility, Interest Rate at Period End, LIBOR Component	0.1875%
Commitment fees for undrawn credit facility	0.375%
Revolving credit facility | Minimum
Debt Disclosure [Line Items]
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR	1.50%
Credit facility interest rate option two, applicable margin rate	0.50%
Commitment fees for undrawn credit facility	0.375%
Required covenant, current ratio	1.0
Revolving credit facility | Maximum
Debt Disclosure [Line Items]
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR	2.50%
Credit facility interest rate option two, applicable margin rate	1.50%
Commitment fees for undrawn credit facility	0.50%
Required covenant, debt to EBITDAX ratio	4.25
Revolving credit facility | through maturity | Maximum
Debt Disclosure [Line Items]
Required covenant, debt to EBITDAX ratio	4.0
Revolving credit facility | Letter of Credit
Debt Disclosure [Line Items]
Maximum borrowing capacity	20,000,000
10.375% Senior Notes due 2016
Debt Disclosure [Line Items]
Write off of deferred debt issuance cost		10,000,000
Cash paid to repurchase principal		330,900,000
Loss on extinguishment of debt, gross			29,200,000
7.25% Senior Notes due 2019
Debt Disclosure [Line Items]
Annual interest rate	7.25%			7.25%
7.25% Senior Notes due 2019 | (Beginning in April 2015)
Debt Disclosure [Line Items]
Debt Instrument, Redemption Price, Percentage	103.625%
7.25% Senior Notes due 2019 | (June 2017 and thereafter)
Debt Disclosure [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
8.50% Senior Notes due 2020
Debt Disclosure [Line Items]
Annual interest rate	8.50%
Debt Proceeds Used For Cash Consideration, Business Acquisition		$ 380,000,000