Derivative Activities - Effects of Cash Flow Hedges and Other Hedges on Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative Instruments Gain Loss [Line Items]
Change in Hedge Derivative Fair Value	$ (6,890)		$ 119,182		$ 275,817
Change in unrealized deferred hedging gains, tax effect	2,687		(47,466)		(104,464)
Change in Hedge Derivative Fair value, effects of Cash flow hedges on accumulated other comprehensive income (loss) total	(4,203)	[1]	71,716	[1]	171,353	[1]
Realized Gain Reclassified from AOCI into Revenue, Income taxes	(46,973)	[2]	(91,871)	[2]	50,005
Realized gain on hedge derivative contract settlements reclassified into earnings from other comprehensive income, net of taxes	73,470	[2]	144,434	[2]
Swaps
Derivative Instruments Gain Loss [Line Items]
Change in Hedge Derivative Fair Value	125		46,371
Realized Gain Reclassified from OCI into Revenue	15,171	[2]	78,779	[2]
Put options
Derivative Instruments Gain Loss [Line Items]
Change in Hedge Derivative Fair Value			(1,955)
Realized Gain Reclassified from OCI into Revenue			(1,955)	[2]
Collars
Derivative Instruments Gain Loss [Line Items]
Change in Hedge Derivative Fair Value	(7,015)		74,766
Realized Gain Reclassified from OCI into Revenue	$ 105,272	[2]	$ 159,481	[2]

[1] Amounts are net of income tax benefit of $2,687 for the year ended December 31, 2013 compared to income tax expense of $47,466 for the year ended December 31, 2012 and income tax expense of $104,464 for the twelve months ended December 31, 2011.

[2] For realized gains upon contract settlement, the reduction in AOCI is offset by an increase in natural gas, NGLs and oil sales. For realized losses upon contract settlement, the increase in AOCI is offset by a decrease in natural gas, NGLs and oil sales.