SUPPLEMENTAL INFORMATION ON OIL AND NATURAL GAS OPERATIONS - UNAUDITED - Financial Data Related to Oil and Gas Producing Activities (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / Mcfe	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) $ / Mcfe	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) $ / Mcfe	Dec. 31, 2015 USD ($) $ / Mcfe	Dec. 31, 2014 USD ($) $ / Mcfe
Accumulated DD&A:
Balance, beginning of year				$ (8,603,955)					$ (8,603,955)
Provision for DD&A									(220,079)	$ (281,688)	$ (340,006)
Foreign currency translation adjustment									(6,073)	2,605	2,801
Write-down of oil and gas properties	$ (73,094)	$ (36,484)	$ (118,649)	(129,204)	$ (351,062)	$ (295,679)	$ (224,294)	$ (491,412)	(357,431)	(1,362,447)	(351,192)
Balance, end of year	(9,178,442)				(8,603,955)				(9,178,442)	(8,603,955)
Net proved oil and gas properties	437,794				771,943				437,794	771,943
Costs incurred during the year (expensed):
Lease operating expenses									79,650	100,139	176,495
Transportation, processing and gathering expenses									27,760	58,847	64,951
Production taxes									3,148	6,877	12,151
Accretion expense									40,229	25,988	28,411
Asset retirement costs included in development cost	(4,461)				(43,901)				(4,461)	(43,901)	(20,305)
United States
Oil and gas properties – United States, proved and unevaluated:
Balance, beginning of year				9,773,457				9,348,054	9,773,457	9,348,054	8,517,873
Costs incurred during the year (capitalized):
Acquisition costs, net of sales of unevaluated properties									3,923	(14,158)	44,634
Exploratory costs									17,891	104,169	270,850
Development costs									102,665	266,982	438,334
Salaries, general and administrative costs									21,753	27,984	33,975
Interest									26,634	41,339	45,722
Less: overhead reimbursements									(521)	(913)	(3,334)
Total costs incurred during the year, net of divestitures									172,345	425,403	830,181
Balance, end of year	9,945,802				9,773,457				9,945,802	9,773,457	9,348,054
Accumulated DD&A:
Balance, beginning of year				(8,561,472)				(6,970,631)	(8,561,472)	(6,970,631)	(5,908,760)
Provision for DD&A									(215,737)	(277,088)	(335,987)
Write-down of oil and gas properties									(357,079)	(1,314,817)	(351,192)
Sale of proved properties									0	1,064	(374,692)
Balance, end of year	(9,134,288)				(8,561,472)				(9,134,288)	(8,561,472)	(6,970,631)
Net proved oil and gas properties	$ 811,514				$ 1,211,985				$ 811,514	$ 1,211,985	$ 2,377,423
DD&A per Mcfe | $ / Mcfe	2.68				3.19				2.68	3.19	3.59
Costs incurred during the year (expensed):
Lease operating expenses									$ 79,650	$ 100,139	$ 176,495
Transportation, processing and gathering expenses									27,760	58,847	64,951
Production taxes									3,148	6,877	12,151
Accretion expense									40,229	25,988	28,411
Expensed costs - United States									150,787	191,851	282,008
CANADA
Oil and gas properties – United States, proved and unevaluated:
Balance, beginning of year				42,484				36,579	42,484	36,579	10,583
Costs incurred during the year (capitalized):
Acquisition costs									(498)	(2,862)	6,956
Exploratory costs									2,168	8,767	19,040
Total costs incurred during the year, net of divestitures									1,670	5,905	25,996
Balance, end of year	$ 44,154				$ 42,484				44,154	42,484	36,579
Accumulated DD&A:
Balance, beginning of year				$ (42,484)				$ 0	(42,484)	0	0
Foreign currency translation adjustment									(1,318)	5,146	0
Write-down of oil and gas properties									(352)	(47,630)	0
Balance, end of year	(44,154)				(42,484)				(44,154)	(42,484)	0
Net proved oil and gas properties	$ 0				$ 0				$ 0	$ 0	$ 36,579