Supplemental Information on Oil and Natural Gas Operations - Unaudited - Financial Data Related to Oil and Gas Producing Activities (Detail) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015 USD ($) $ / Mcfe	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) $ / Mcfe	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) $ / Mcfe	Dec. 31, 2014 USD ($) $ / Mcfe	Dec. 31, 2013 USD ($) $ / Mcfe
Accumulated DD&A:
Balance, beginning of year					$ (6,970,631)					$ (6,970,631)
Provision for DD&A										(281,688)	$ (340,006)	$ (350,574)
Foreign currency translation adjustment										2,605	2,801	667
Write-down of oil and gas properties		$ (351,062)	$ (295,679)	$ (224,294)	(491,412)	$ (304,062)	$ (47,130)	$ 0	$ 0	(1,362,447)	(351,192)	0
Balance, end of year		(8,603,955)				(6,970,631)				(8,603,955)	(6,970,631)
Net proved oil and gas properties		771,943				1,846,637				771,943	1,846,637
Lease operating expenses										100,139	176,495	201,153
Transportation, processing and gathering expenses										58,847	64,951	42,172
Production taxes										6,877	12,151	15,029
Accretion expense										25,988	28,411	33,575
United States [Member]
Oil and gas properties, proved and unevaluated:
Balance, beginning of year					9,348,054				8,517,873	9,348,054	8,517,873	7,692,261
Costs incurred during the year (capitalized):
Acquisition costs, net of sales of unevaluated properties										(14,158)	44,634	70,903
Exploratory costs										104,169	270,850	297,113
Development costs	[1]									266,982	438,334	378,242
Salaries, general and administrative costs										27,984	33,975	32,815
Interest										41,339	45,722	46,860
Less: overhead reimbursements										(913)	(3,334)	(321)
Total costs incurred during the year										425,403	830,181	825,612
Balance, end of year		9,773,457				9,348,054				9,773,457	9,348,054	8,517,873
Accumulated DD&A:
Balance, beginning of year					(6,970,631)				(5,908,760)	(6,970,631)	(5,908,760)	(5,510,166)
Provision for DD&A										(277,088)	(335,987)	(346,827)
Write-down of oil and gas properties										(1,314,817)	(351,192)	0
Sale of proved properties										1,064	(374,692)	(51,767)
Balance, end of year		(8,561,472)				(6,970,631)				(8,561,472)	(6,970,631)	(5,908,760)
Net proved oil and gas properties		$ 1,211,985				$ 2,377,423				$ 1,211,985	$ 2,377,423	$ 2,609,113
DD&A per Mcfe | $ / Mcfe		3.19				3.59				3.19	3.59	3.43
Lease operating expenses										$ 100,139	$ 176,495	$ 201,153
Transportation, processing and gathering expenses										58,847	64,951	42,172
Production taxes										6,877	12,151	15,029
Accretion expense										25,988	28,411	33,575
Expensed costs - United States										191,851	282,008	291,929
Canada [Member]
Oil and gas properties, proved and unevaluated:
Balance, beginning of year					36,579				10,583	36,579	10,583	0
Costs incurred during the year (capitalized):
Acquisition costs										(2,862)	6,956	8,764
Exploratory costs										8,767	19,040	1,819
Total costs incurred during the year										5,905	25,996	10,583
Balance, end of year		$ 42,484				$ 36,579				42,484	36,579	10,583
Accumulated DD&A:
Balance, beginning of year					$ 0				$ 0	0	0	0
Foreign currency translation adjustment										5,146	0	0
Write-down of oil and gas properties										(47,630)	0	0
Balance, end of year		(42,484)				0				(42,484)	0	0
Net proved oil and gas properties		$ 0				$ 36,579				$ 0	$ 36,579	$ 10,583

[1] Includes capitalized asset retirement costs of ($43,901), ($20,305) and $54,737, respectively.