STOCK-BASED COMPENSATION (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Stock-based compensation
Total stock-based compensation costs	$ 2,631	[1]	$ 4,828	[1],[2]	$ 4,379	[1]	$ 11,953	[1]
Less: stock-based compensation costs capitalized	(884)	[1]	(1,631)	[1],[2]	(1,803)	[1]	(4,595)	[1]
Stock-based compensation costs expensed	1,747	[1]	3,197	[1],[2]	2,576	[1]	7,358	[1]
Unamortized stock-based compensation costs	10,294	[1],[3]			10,294	[1],[3]
Weighted average amortization period remaining					1 year 3 months 18 days	[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)					(237,100)
Options outstanding at end of period (in shares)	394,106				394,106
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)					$ 13.86
Options outstanding, end of period (in dollars per share)	$ 19.23				$ 19.23
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)	394,106				394,106				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	1,605		3,210		3,176		7,445
Less: stock-based compensation costs capitalized	(604)		(1,172)		(1,403)		(2,994)
Stock-based compensation costs expensed	1,001		2,038		1,773		4,451
Unamortized stock-based compensation costs	5,887	[3]			5,887	[3]
Weighted average amortization period remaining					1 year 2 months 12 days
Share-based compensation plan activity
Unvested at beginning of period (in shares)					2,790,542
Awarded (in shares)					407,202
Vested (in shares)					(905,882)
Forfeited (in shares)					(297,954)
Unvested at end of period (in shares)	1,993,908	[5]			1,993,908	[5]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)					$ 10.23
Awarded (in dollars per share)					$ 2.22
Vested (in dollars per share)					$ 14.41
Forfeited (in dollars per share)					$ 10.29
Unvested at end of period (in dollars per share)	$ 6.69				$ 6.69
Vest Date Fair Value
Vested, Vest Date Fair Value					2,455
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)	436,956				436,956
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	598		1,105		600		2,733
Less: stock-based compensation costs capitalized	(122)		(241)		(128)		(714)
Stock-based compensation costs expensed	476		864		472		2,019
Unamortized stock-based compensation costs	2,294	[3]			2,294	[3]
Weighted average amortization period remaining					1 year 6 months
Share-based compensation plan activity
Unvested at beginning of period (in shares)					1,511,140
Awarded (in shares)					0
Vested (in shares)					(63,840)
Forfeited (in shares)					(170,300)
Unvested at end of period (in shares)	1,277,000	[6]			1,277,000	[6]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)					$ 8.48
Awarded (in dollars per share)					$ 0.00
Vested (in dollars per share)					$ 18.11
Forfeited (in dollars per share)					$ 9.33
Unvested at end of period (in dollars per share)	$ 7.89				$ 7.89
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)	598,500				598,500
Phantom Stock Units
Stock-based compensation
Total stock-based compensation costs	428		513		603		1,775
Less: stock-based compensation costs capitalized	(158)		(218)		(272)		(887)
Stock-based compensation costs expensed	270		295		331		888
Unamortized stock-based compensation costs	2,113	[3]			2,113	[3]
Weighted average amortization period remaining					1 year 7 months 6 days
Share-based compensation plan activity
Unvested at beginning of period (in shares)					1,924,819
Awarded (in shares)					67,000
Vested (in shares)					(343,583)
Forfeited (in shares)					(184,139)
Unvested at end of period (in shares)	1,464,097	[7]			1,464,097	[7]
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in dollars per share)					$ 6.75
Awarded (in dollars per share)					$ 3.51
Vested (in dollars per share)					$ 7.07
Forfeited (in dollars per share)					$ 7.54
Unvested at end of period (in dollars per share)	$ 6.43				$ 6.43
Vest Date Fair Value
Vested, Vest Date Fair Value					1,127
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)	122,509				122,509
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)	270,000				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)	466,588				466,588
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)	493,000				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)	45,000				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)	67,000				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	$ 20		$ 100		$ 100		$ 200

[1] Forest also maintains an employee stock purchase plan (which is not included in the table) under which $.02 million and $.1 million of compensation cost was recognized for the three and six months ended June 30, 2014, respectively, and $.1 million and $.2 million of compensation cost was recognized for the three and six months ended June 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 June 30, 2014, 436,956 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 June 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 June 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 six months ended June 30, 2014 were settled in cash. Of the unvested phantom stock units as of June 30, 2014, (i) 122,509 were granted in 2011 and 466,588 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.