STOCK-BASED COMPENSATION (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended				1 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Jun. 30, 2011 Stock Options	Jun. 30, 2010 Stock Options	Jun. 30, 2011 Stock Options	Jun. 30, 2010 Stock Options	Jun. 30, 2011 Restricted Stock	Jun. 30, 2010 Restricted Stock	Jun. 30, 2011 Restricted Stock	Jun. 30, 2010 Restricted Stock	Jun. 30, 2011 Phantom Stock Units	Jun. 30, 2010 Phantom Stock Units	Jun. 30, 2011 Phantom Stock Units	Jun. 30, 2010 Phantom Stock Units	Jun. 30, 2011 Performance Units	Jun. 30, 2011 Performance Units	Jun. 30, 2010 Performance Units	Jun. 30, 2011 Performance Units	Jun. 30, 2010 Performance Units	Jun. 30, 2011 Lone Pine Plan	Jun. 30, 2011 Forest Oil Plans	Jun. 30, 2011 Cash-based long-term incentive award	Jun. 30, 2011 Time-based component of cash-based long-term incentive award	Jun. 30, 2011 Performance-based component of cash-based long-term incentive award	Jun. 30, 2011 Employee Stock Purchase Plan	Jun. 30, 2010 Employee Stock Purchase Plan	Jun. 30, 2011 Employee Stock Purchase Plan	Jun. 30, 2010 Employee Stock Purchase Plan	Jun. 30, 2011 Lone Pine Resources Inc
Stock-based compensation
Total stock-based compensation costs	$ 4,271,000	$ 7,902,000	$ 12,792,000	$ 16,213,000		$ 278,000	$ 8,000	$ 441,000	$ 230,000	$ 4,782,000	$ 5,892,000	$ 11,151,000	$ 12,713,000	$ (1,588,000)	$ 1,261,000	$ (270,000)	$ 2,529,000		$ 799,000	$ 741,000	$ 1,470,000	$ 741,000			$ 9,000			$ 100,000	$ 100,000	$ 300,000	$ 300,000
Less: stock-based compensation costs capitalized	(1,455,000)	(2,582,000)	(4,934,000)	(5,955,000)		(155,000)	(3,000)	(226,000)	(96,000)	(1,937,000)	(1,806,000)	(4,528,000)	(4,497,000)	902,000	(543,000)	277,000	(1,132,000)		(265,000)	(230,000)	(457,000)	(230,000)
Stock-based compensation costs expensed	2,816,000	5,320,000	7,858,000	10,258,000		123,000	5,000	215,000	134,000	2,845,000	4,086,000	6,623,000	8,216,000	(686,000)	718,000	7,000	1,397,000		534,000	511,000	1,013,000	511,000
Unamortized stock-based compensation costs	59,487,000		59,487,000							40,084,000		40,084,000		8,912,000		8,912,000		10,491,000	10,491,000		10,491,000				500,000
Weighted average amortization period remaining (in years)			2.2									2.4				1.7					2.2
Period after which cash payment will be made dependent on change in value of entity's common stock (in years)																										3	3
Period for which change in fair value of entity's common stock is measured (in years)																										3	3
Stock option activity
Options outstanding at beginning of period (in shares)			1,327,695
Exercised (in shares)			18,306
Cancelled (in shares)			1,200
Options outstanding at end of period (in shares)	1,308,189		1,308,189
Stock Options, Weighted Average Exercise Price
Options outstanding, beginning of period (in dollars per share)			$ 21.67
Exercised (in dollars per share)	$ 19.05		$ 19.05
Cancelled (in dollars per share)	$ 42.41		$ 42.41
Options outstanding, end of period (in dollars per share)	$ 21.69		$ 21.69
Stock Options, Aggregate Intrinsic Value
Aggregate intrinsic value for stock options at beginning of the period			22,531,000
Aggregate intrinsic value for stock options at end of the period	9,381,000		9,381,000
Aggregate intrinsic value for stock options exercised			303,000
Stock Options, Number of Options Exercisable
Options outstanding, exercisable number (in shares)	1,308,189		1,308,189		1,283,232
Share-based compensation plan activity
Unvested stock, beginning of period (in shares)												2,272,321				510,609					264,500
Awarded (in shares)												1,006,514				460,885		226,000			226,000		460,385	500
Vested (in shares)												(593,581)				(39,787)
Forfeited (in shares)												(38,205)				(3,122)
Unvested stock, end of period (in shares)										2,647,049		2,647,049		928,585		928,585		490,500	490,500		490,500
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)												$ 32.71				$ 24.79					$ 31.63
Awarded (in dollars per share)												$ 27.28				$ 12.38		$ 27.53			$ 27.53
Vested (in dollars per share)												$ 61.92				$ 62.65
Forfeited (in dollars per share)										$ 26.62		$ 26.62		$ 18.06		$ 18.06
Unvested at end of period (in dollars per share)										$ 24.18		$ 24.18		$ 17.03		$ 17.03		$ 29.74	$ 29.74		$ 29.74
Vest Date Fair Value
Vested, Vest Date fair Value												18,042,000				1,203,000
Number of shares of common stock to be received for each performance unit (in shares)																		1
Actual number of shares deliverable for each performance unit awarded, low end of range (as a percent)																		0.00%
Actual number of shares deliverable for each performance unit awarded, high end of range (as a percent)																		200.00%
Performance period (in months)																		Thirty-six month
Unvested units that can be settled in cash, shares of common stock, or a combination of both (in shares)														248,321		248,321
Unvested units that can only be settled in cash (in shares)														680,264		680,264
Vested units settled in common stock (in shares)																5,500
Vested units settled in cash (in shares)																34,287
Unamortized stock-based compensation cost based on the closing price of the common stock	4,600,000		4,600,000
Unamortized stock-based compensation cost based on the closing price of the common stock.																																$ 4,300,000