STOCK-BASED COMPENSATION (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Stock-based compensation
Total stock-based compensation costs	$ 1,748	[1]	$ 7,125	[1],[2]
Less: stock-based compensation costs capitalized	(919)	[1]	(2,964)	[1],[2]
Stock-based compensation costs expensed	829	[1]	4,161	[1],[2]
Unamortized stock-based compensation costs	11,714	[1],[3]
Weighted average amortization period remaining	1 year 6 months	[1]
Stock option activity
Options outstanding at beginning of period (in shares)	631,206
Granted (in shares)	0
Exercised (in shares)	0
Cancelled (in shares)	(171,377)
Options outstanding at end of period (in shares)	459,829
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)	$ 13.88
Options outstanding, end of period (in dollars per share)	$ 18.45
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]
Stock Options, Number of Options Exercisable
Options outstanding, exercisable number (in shares)	459,829				631,206
One-time Employee Termination Benefits
Stock-based compensation
Total stock-based compensation costs			2,000
Stock-based compensation costs expensed			1,000
Restricted Stock
Stock-based compensation
Total stock-based compensation costs	1,571		4,235
Less: stock-based compensation costs capitalized	(799)		(1,822)
Stock-based compensation costs expensed	772		2,413
Unamortized stock-based compensation costs	6,887	[3]
Weighted average amortization period remaining	1 year 3 months 18 days
Share-based compensation plan activity
Unvested at beginning of period (in shares/units)	2,790,542
Awarded (in shares/units)	1,000
Vested (in shares/units)	(349,118)
Forfeited (in shares/units)	(217,173)
Unvested at end of period (in shares/units)	2,225,251	[5]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share/unit)	$ 10.23
Awarded (in dollars per share/unit)	$ 1.82
Vested (in dollars per share/unit)	$ 8.68
Forfeited (in dollars per share/unit)	$ 9.85
Unvested at end of period (in dollars per share/unit)	$ 10.51
Vest Date Fair Value
Vested, Vest Date Fair Value	1,166
Restricted Stock | Cliff Vest On Third Anniversary of Award Date
Vest Date Fair Value
Award vesting period (in years)	3 years
Restricted Stock | Granted in 2013 | Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant
Share-based compensation plan activity
Unvested at end of period (in shares/units)	486,385
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	33.33333%
Award vesting period (in years)	3 years
Performance Units
Stock-based compensation
Total stock-based compensation costs	2		1,628
Less: stock-based compensation costs capitalized	(6)		(473)
Stock-based compensation costs expensed	(4)		1,155
Unamortized stock-based compensation costs	2,749	[3]
Weighted average amortization period remaining	1 year 8 months 12 days
Share-based compensation plan activity
Unvested at beginning of period (in shares/units)	1,511,140
Awarded (in shares/units)	0
Vested (in shares/units)	0
Forfeited (in shares/units)	(170,300)
Unvested at end of period (in shares/units)	1,340,840	[6]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share/unit)	$ 8.48
Awarded (in dollars per share/unit)	$ 0.00
Vested (in dollars per share/unit)	$ 0.00
Forfeited (in dollars per share/unit)	$ 9.33
Unvested at end of period (in dollars per share/unit)	$ 8.38
Vest Date Fair Value
Vested, Vest Date Fair Value	0
Performance period for cash settled and share settled performance units	36 months
Performance Units | Granted in 2013 | Cash-settled
Share-based compensation plan activity
Unvested at end of period (in shares/units)	598,500
Phantom Stock Units
Stock-based compensation
Total stock-based compensation costs	175		1,262
Less: stock-based compensation costs capitalized	(114)		(669)
Stock-based compensation costs expensed	61		593
Unamortized stock-based compensation costs	2,078	[3]
Weighted average amortization period remaining	1 year 8 months 12 days
Share-based compensation plan activity
Unvested at beginning of period (in shares/units)	1,924,819
Awarded (in shares/units)	67,000
Vested (in shares/units)	(313,287)
Forfeited (in shares/units)	(139,128)
Unvested at end of period (in shares/units)	1,539,404	[7]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share/unit)	$ 6.75
Awarded (in dollars per share/unit)	$ 3.51
Vested (in dollars per share/unit)	$ 7.07
Forfeited (in dollars per share/unit)	$ 7.19
Unvested at end of period (in dollars per share/unit)	$ 6.51
Vest Date Fair Value
Vested, Vest Date Fair Value	1,065
Phantom Stock Units | Vest Over Four Year Period | First Anniversary of the Grant Date
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	10.00%
Phantom Stock Units | Vest Over Four Year Period | Second Anniversary of the Grant Date
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	20.00%
Phantom Stock Units | Vest Over Four Year Period | Third Anniversary of the Grant Date
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	30.00%
Phantom Stock Units | Vest Over Four Year Period | Fourth Anniversary Of the Grant Date
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	40.00%
Phantom Stock Units | Granted in 2011 | Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant
Share-based compensation plan activity
Unvested at end of period (in shares/units)	136,619
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	33.33333%
Award vesting period (in years)	3 years
Phantom Stock Units | Granted in 2012 | Vest Over Four Year Period
Share-based compensation plan activity
Unvested at end of period (in shares/units)	270,000
Vest Date Fair Value
Award vesting period (in years)	4 years
Phantom Stock Units | Granted in 2013 | Vesting Schedule One-Third On Each Of the First Three Anniversary Dates of the Grant
Share-based compensation plan activity
Unvested at end of period (in shares/units)	527,785
Vest Date Fair Value
Vesting rate per anniversary date of grant (as a percent)	33.33333%
Award vesting period (in years)	3 years
Phantom Stock Units | Granted in 2013 | Cliff Vest On Third Anniversary of Award Date
Share-based compensation plan activity
Unvested at end of period (in shares/units)	493,000
Vest Date Fair Value
Award vesting period (in years)	3 years
Phantom Stock Units | Granted in 2013 | Vest Over Four Year Period
Share-based compensation plan activity
Unvested at end of period (in shares/units)	45,000
Vest Date Fair Value
Award vesting period (in years)	4 years
Phantom Stock Units | Granted in 2014 | Cliff Vest On Third Anniversary of Award Date
Share-based compensation plan activity
Unvested at end of period (in shares/units)	67,000
Vest Date Fair Value
Award vesting period (in years)	3 years
Employee Stock Purchase Plan
Stock-based compensation
Total stock-based compensation costs	$ 30		$ 100

[1] Forest also maintains an employee stock purchase plan (which is not included in the table) under which $.03 million and $.1 million of compensation cost was recognized for the three month periods ended March 31, 2014, and 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 March 31, 2014, 486,385 shares, which were granted in 2013, vest in one-third increments on each of the first three anniversary dates of the grant. All other unvested shares of restricted stock cliff vest on the third anniversary of the date of grant.

[6] Of the unvested performance units as of March 31, 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 March 31, 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 three months ended March 31, 2014 were settled in cash. Of the unvested phantom stock units as of March 31, 2014, (i) 136,619 were granted in 2011 and 527,785 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, (iii) and 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.