STOCK-BASED COMPENSATION (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended					3 Months Ended				9 Months Ended						3 Months Ended			9 Months Ended				3 Months Ended			9 Months Ended													3 Months Ended		9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013	Mar. 31, 2013 One-time Employee Termination Benefits	Sep. 30, 2014 Restricted Stock		Sep. 30, 2013 Restricted Stock	Sep. 30, 2014 Restricted Stock		Sep. 30, 2013 Restricted Stock	Sep. 30, 2014 Restricted Stock Cliff Vest On Third Anniversary of Award Date	Sep. 30, 2014 Restricted Stock Granted in 2013 Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant	Sep. 30, 2014 Restricted Stock Granted in 2014 Vesting Schedule - first anniversary of the date of the grant, [Member]	Sep. 30, 2014 Performance Units		Sep. 30, 2013 Performance Units	Sep. 30, 2014 Performance Units		Sep. 30, 2013 Performance Units	Sep. 30, 2014 Performance Units Granted in 2013 Cash-settled	Sep. 30, 2014 Phantom Stock Units		Sep. 30, 2013 Phantom Stock Units	Sep. 30, 2014 Phantom Stock Units		Sep. 30, 2013 Phantom Stock Units	Sep. 30, 2014 Phantom Stock Units Vest Over Four Year Period First Anniversary of the Grant Date	Sep. 30, 2014 Phantom Stock Units Vest Over Four Year Period Second Anniversary of the Grant Date	Sep. 30, 2014 Phantom Stock Units Vest Over Four Year Period Third Anniversary of the Grant Date	Sep. 30, 2014 Phantom Stock Units Vest Over Four Year Period Fourth Anniversary Of the Grant Date	Sep. 30, 2014 Phantom Stock Units Granted in 2011 Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant	Sep. 30, 2014 Phantom Stock Units Granted in 2012 Vest Over Four Year Period	Sep. 30, 2014 Phantom Stock Units Granted in 2013 Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant	Sep. 30, 2014 Phantom Stock Units Granted in 2013 Cliff Vest On Third Anniversary of Award Date	Sep. 30, 2014 Phantom Stock Units Granted in 2013 Vest Over Four Year Period	Sep. 30, 2014 Phantom Stock Units Granted in 2014 Cliff Vest On Third Anniversary of Award Date	Sep. 30, 2014 Employee Stock Purchase Plan	Sep. 30, 2013 Employee Stock Purchase Plan	Sep. 30, 2014 Employee Stock Purchase Plan	Sep. 30, 2013 Employee Stock Purchase Plan
Stock-based compensation
Total stock-based compensation costs	$ 1,876	[1]	$ 3,707	[1],[2]	$ 6,255	[1]	$ 15,660	[1]		$ 2,000	$ 1,419		$ 1,644	$ 4,595		$ 9,089				$ 631		$ 301	$ 1,231		$ 3,034		$ (174)		$ 1,762	$ 429		$ 3,537											$ 10	$ 0	$ 100	$ 200
Less: stock-based compensation costs capitalized	(561)	[1]	(1,950)	[1],[2]	(2,364)	[1]	(6,545)	[1]			(491)		(877)	(1,894)		(3,871)				(118)		(245)	(246)		(959)		48		(828)	(224)		(1,715)
Stock-based compensation costs expensed	1,315	[1]	1,757	[1],[2]	3,891	[1]	9,115	[1]		1,000	928		767	2,701		5,218				513		56	985		2,075		(126)		934	205		1,822
Unamortized stock-based compensation costs	7,512	[1],[3]			7,512	[1],[3]					4,706	[3]		4,706	[3]					1,811	[3]		1,811	[3]			995	[3]		995	[3]
Weighted average amortization period remaining					1 year 1 month 6 days	[1]								1 year 1 day									1 year 2 months 12 days							1 year 6 months
Stock option activity
Options outstanding at beginning of period (in shares)					631,206
Granted (in shares)					0
Exercised (in shares)					0
Cancelled (in shares)					(267,274)
Options outstanding at end of period (in shares)	363,932				363,932
Stock Options, Weighted Average Exercise Price
Options outstanding, beginning of period (in dollars per share)					$ 17.21
Granted (in dollars per share)					$ 0.00
Exercised (in dollars per share)					$ 0.00
Cancelled (in dollars per share)					$ 14.31
Options outstanding, end of period (in dollars per share)	$ 19.34				$ 19.34
Stock Options, Aggregate Intrinsic Value
Aggregate intrinsic value for stock options at beginning of the period					0	[4]
Aggregate intrinsic value for stock options exercised					0	[4]
Aggregate intrinsic value for stock options at end of the period	0	[4]			0	[4]
Stock Options, Number of Options Exercisable
Options outstanding, exercisable number (in shares)	363,932				363,932				631,206
Share-based compensation plan activity
Unvested at beginning of period (in shares)														2,790,542					405,702				1,511,140			598,500				1,924,819
Awarded (in shares)														407,202									0							67,000
Vested (in shares)														(929,682)									(63,840)							(345,617)
Forfeited (in shares)														(300,804)									(170,300)							(185,155)
Unvested at end of period (in shares)											1,967,258	[5]		1,967,258	[5]			436,056	405,702	1,277,000	[6]		1,277,000	[6]		598,500	1,461,047	[7]		1,461,047	[7]						122,393	270,000	463,654	493,000	45,000	67,000
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)														$ 10.23									$ 8.48							$ 6.75
Awarded (in dollars per share)														$ 2.22									$ 0.00							$ 3.51
Vested (in dollars per share)														$ 14.58									$ 18.11							$ 7.05
Forfeited (in dollars per share)														$ 10.26									$ 9.33							$ 7.54
Unvested at end of period (in dollars per share)											$ 6.52			$ 6.52						$ 7.89			$ 7.89				$ 6.43			$ 6.43
Vest Date Fair Value
Vested, Vest Date Fair Value														$ 2,504									$ 0							$ 1,131
Vesting rate per anniversary date of grant (as a percent)																		33.33333%															10.00%	20.00%	30.00%	40.00%	33.33333%		33.33333%
Award vesting period (in years)																	3 years	3 years																			3 years	4 years	3 years	3 years	4 years	3 years
Performance period for cash settled and share settled performance units																							36 months

[1] Forest also maintains an employee stock purchase plan (which is not included in the table) under which $.01 million and $.1 million of compensation cost was recognized for the three and nine months ended September 30, 2014, respectively, and $.04 million and $.2 million of compensation cost was recognized for the three and nine months ended September 30, 2013, respectively.

[2] In connection with the divestiture of the South Texas oil and natural gas properties in the first quarter of 2013, Forest incurred $2.0 million ($1.0 million net of capitalized amounts) in stock-based compensation costs due to accelerated vesting of involuntarily terminated employees’ awards. See Note 5 for more information regarding this divestiture.

[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] 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.

[5] Of the unvested restricted stock as of September 30, 2014, (i) 436,056 shares, which were granted in 2013, vest in one-third increments on each of the first three anniversary dates of the grant, (ii) 405,702 shares, which were granted in 2014, vest on the first anniversary of the date of the grant, and (iii) all remaining unvested shares of restricted stock cliff vest on the third anniversary of the date of grant.

[6] Of the unvested performance units as of September 30, 2014, 598,500, which were granted in 2013, are cash-based and the remaining unvested performance units are share-based. For both cash- and share-based performance units, the actual settlement amount is dependent upon Forest’s relative total shareholder return in comparison to a specified peer group over a thirty-six month performance period. The cash-based performance units are accounted for as a liability within the Condensed Consolidated Financial Statements.

[7] All of the unvested phantom stock units as of September 30, 2014 must be settled in cash. The phantom stock units have been accounted for as a liability within the Condensed Consolidated Financial Statements. All of the phantom stock units that vested during the nine months ended September 30, 2014 were settled in cash. Of the unvested phantom stock units as of September 30, 2014, (i) 122,393 were granted in 2011 and 463,654 were granted in 2013 and vest in one-third increments on each of the first three anniversaries of the grant date, (ii) 493,000 were granted in 2013 and 67,000 were granted in 2014 and cliff vest on the third anniversary of the grant date, and (iii) 270,000 were granted in 2012 and 45,000 were granted in 2013 and vest over a four-year period in accordance with the following schedule: (a) 10% on the first anniversary of the grant date; (b) 20% on the second anniversary of the grant date; (c) 30% on the third anniversary of the grant date; and (d) 40% on the fourth anniversary of the grant date.