STOCK-BASED COMPENSATION (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Stock-based compensation
Total stock-based compensation costs					$ 18,383	[1],[2]	$ 22,318	[1]	$ 35,104	[1]
Less: stock-based compensation costs capitalized					(7,808)	[1],[2]	(7,353)	[1]	(14,867)	[1]
Stock-based compensation costs expensed					10,575	[1],[2]	14,965	[1]	20,237	[1]
Unamortized stock-based compensation costs as of December 31, 2013					17,790	[1],[2],[3]
Weighted average amortization period remaining as of December 31, 2013 (in years)					1 year 7 months 6 days	[1],[2]
Stock option activity
Options outstanding at beginning of period (in shares)	1,957,900		1,327,695		870,816		1,766,587		1,327,695
Granted (in shares)	0		0		0		0
Exercised (in shares)	(161,834)		(29,711)		0		0
Cancelled (in shares)	(29,479)		(13,273)		(239,610)		(895,771)
Spin-off adjustment (in shares)			673,189	[4]
Options outstanding at end of period (in shares)	1,766,587		1,957,900		631,206		870,816		1,766,587
Stock Options, Weighted Average Exercise Price
Options outstanding, beginning of period (in dollars per share)	$ 14.29		$ 21.67		$ 17.86		$ 14.55		$ 21.67
Granted (in dollars per share)	$ 0		$ 0		$ 0		$ 0
Exercised (in dollars per share)	$ 11.32		$ 18.55		$ 0		$ 0
Cancelled (in dollars per share)	$ 14.86		$ 25.11		$ 19.55		$ 11.33
Options outstanding, end of period (in dollars per share)	$ 14.55		$ 14.29		$ 17.21		$ 17.86		$ 14.55
Stock Options, Aggregate Intrinsic Value
Aggregate intrinsic value for stock options at beginning of the period	187	[5]	22,531	[5]	0	[5]	2,731	[5]	22,531	[5]
Aggregate intrinsic value for stock options exercised	634	[5]	331	[5]	0	[5]	0	[5]
Aggregate intrinsic value for stock options at end of the period	2,731	[5]	187	[5]	0	[5]	0	[5]	2,731	[5]
Stock Options, Number of Options Exercisable
Options outstanding, exercisable number (in shares)	1,766,587		1,957,900		631,206		870,816		1,766,587		1,283,232
One-time Employee Termination Benefits
Stock-based compensation
Total stock-based compensation costs					4,900
Stock-based compensation costs expensed					2,100
Stock Options
Stock-based compensation
Total stock-based compensation costs					0		0		1,536
Less: stock-based compensation costs capitalized					0		0		(663)
Stock-based compensation costs expensed					0		0		873
Unamortized stock-based compensation costs as of December 31, 2013					0
Weighted average amortization period remaining as of December 31, 2013 (in years)					0 years
Restricted Stock
Stock-based compensation
Total stock-based compensation costs					12,149		14,621		30,234
Less: stock-based compensation costs capitalized					(5,355)		(5,219)		(13,113)
Stock-based compensation costs expensed					6,794		9,402		17,121
Unamortized stock-based compensation costs as of December 31, 2013					9,611
Weighted average amortization period remaining as of December 31, 2013 (in years)					1 year 6 months
Share-based compensation plan activity
Unvested stock, beginning of period (in shares)	2,556,092		2,272,321		2,721,637		2,474,112		2,272,321
Awarded (in shares)	25,700		1,025,782		2,163,877		1,743,757
Vested (in shares)	(48,560)		(610,681)		(1,286,322)		(956,547)
Forfeited (in shares)	(59,120)		(131,330)		(808,650)		(539,685)
Spin-off adjusment (in shares)			0
Vested due to spin-off (in shares)			0
Unvested stock, end of period (in shares)	2,474,112		2,556,092		2,790,542		2,721,637		2,474,112
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)	$ 24.18		$ 32.71		$ 17.64		$ 24.00		$ 32.71
Awarded (in dollars per share)	$ 15.19		$ 27.30		$ 6.04		$ 9.95
Vested (in dollars per share)	$ 28.84		$ 61.33		$ 18.07		$ 19.51
Forfeited (in dollars per share)	$ 23.93		$ 23.51		$ 11.47		$ 18.65
Unvested at end of period (in dollars per share)	$ 24.00		$ 24.18		$ 10.23		$ 17.64		$ 24.00
Vest Date Fair Value
Vested, vest date fair value	595		18,416		6,911		7,667
Performance Units
Stock-based compensation
Total stock-based compensation costs					2,288		6,838		3,178
Less: stock-based compensation costs capitalized					(431)		(1,565)		(957)
Stock-based compensation costs expensed					1,857		5,273		2,221
Unamortized stock-based compensation costs as of December 31, 2013					3,517	[3]
Weighted average amortization period remaining as of December 31, 2013 (in years)					1 year 10 months 24 days
Share-based compensation plan activity
Unvested stock, beginning of period (in shares)	664,240		264,500		939,180		655,120		264,500
Awarded (in shares)	0		226,000		1,182,500		789,500
Vested (in shares)	0		0		(203,240)		(323,760)
Forfeited (in shares)	(9,120)		(41,000)		(407,300)		(181,680)
Spin-off adjusment (in shares)			233,740	[6]
Vested due to spin-off (in shares)			(19,000)	[7]
Unvested stock, end of period (in shares)	655,120		664,240		1,511,140		939,180		655,120
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)	$ 19.52		$ 31.63		$ 15.20		$ 19.50		$ 31.63
Awarded (in dollars per share)	$ 0		$ 27.53		$ 5.47		$ 13.40
Vested (in dollars per share)	$ 0		$ 0		$ 19.60		$ 18.18
Forfeited (in dollars per share)	$ 20.81		$ 29.98		$ 9.68		$ 17.55
Vested due to spin-off (in dollars per share)			$ 20.81
Unvested at end of period (in dollars per share)	$ 19.50		$ 19.52		$ 8.48		$ 15.20		$ 19.50
Vest Date Fair Value
Vested, vest date fair value	0		0		0		0
Vested due to spin-off, vest date fair value			0
Phantom Stock Units
Stock-based compensation
Total stock-based compensation costs					3,946		859		156
Less: stock-based compensation costs capitalized					(2,022)		(569)		(134)
Stock-based compensation costs expensed					1,924		290		22
Unamortized stock-based compensation costs as of December 31, 2013					4,662	[3]
Weighted average amortization period remaining as of December 31, 2013 (in years)					1 year 9 months 18 days
Share-based compensation plan activity
Unvested stock, beginning of period (in shares)	315,024		510,609		1,161,737		1,238,817		510,609
Awarded (in shares)	941,300		500		1,808,701		718,500
Vested (in shares)	(3,505)		(52,587)		(577,201)		(608,543)
Forfeited (in shares)	(14,002)		(25,737)		(468,418)		(187,037)
Spin-off adjusment (in shares)			225,004	[6]
Vested due to spin-off (in shares)			(342,765)	[7]
Unvested stock, end of period (in shares)	1,238,817		315,024		1,924,819		1,161,737		1,238,817
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)	$ 12.15		$ 24.79		$ 9.91		$ 14.32		$ 24.79
Awarded (in dollars per share)	$ 15.08		$ 28.24		$ 6.28		$ 6.73
Vested (in dollars per share)	$ 17.07		$ 60.04		$ 10.60		$ 14.15
Forfeited (in dollars per share)	$ 16.21		$ 19.12		$ 8.03		$ 13.10
Vested due to spin-off (in dollars per share)			$ 15.15
Unvested at end of period (in dollars per share)	$ 14.32		$ 12.15		$ 6.75		$ 9.91		$ 14.32
Vest Date Fair Value
Vested, vest date fair value	43		1,449		2,881		4,511
Vested due to spin-off, vest date fair value			3,246
Employee Stock Purchase Plan
Stock-based compensation
Total stock-based compensation costs					$ 200		$ 400		$ 500
Weighted Average Grant Date Fair Value
Awarded (in dollars per share)					$ 1.29		$ 2.43		$ 5.00

[1] The Company also maintains an employee stock purchase plan (which is not included in the table) under which $.2 million, $.4 million, and $.5 million of compensation costs were recognized for the years ended December 31, 2013, 2012, and 2011, respectively.

[2] In connection with the 2013 divestitures of the South Texas and Texas Panhandle oil and natural gas properties, Forest incurred $4.9 million ($2.1 million net of capitalized amounts) in stock-based compensation costs due to accelerated vesting of involuntarily terminated employees’ awards. See Note 2 for more information regarding these divestitures.

[3] The unamortized stock-based compensation costs for liability-based awards are based on the closing price of Forest’s common stock at the reporting period end.

[4] In conjunction with the spin-off of Lone Pine, both the number of options outstanding and the option exercise prices were adjusted in accordance with antidilution provisions provided in the Stock-based Compensation Plans.

[5] The intrinsic value of a stock option is the amount by which the market value of the underlying stock, as of the date outstanding or exercised, exceeds the exercise price of the option.

[6] In conjunction with the spin-off of Lone Pine, the number of performance units and phantom stock units outstanding was adjusted in accordance with antidilution provisions provided in the Stock-based Compensation Plans. In addition, the initial stock prices used to measure Forest’s total shareholder returns over the performance periods of the performance units were adjusted in accordance with the antidilution provisions provided in the Stock-based Compensation Plans. The number of restricted stock awards outstanding was not adjusted as a result of the spin-off since holders of restricted stock awards received Lone Pine common shares in the spin-off.

[7] In conjunction with the spin-off of Lone Pine, Lone Pine employees were deemed to have been involuntarily terminated under the terms of their phantom stock and performance unit agreements, and, therefore, all such awards held by Lone Pine employees vested on September 30, 2011. The phantom stock awards were settled in cash by Lone Pine. No shares were deliverable under the performance unit agreement. No Forest restricted stock awards were held by Lone Pine employees at the time of the spin-off.