DEBT (Details) (USD $)	12 Months Ended											12 Months Ended						12 Months Ended													0 Months Ended	1 Months Ended					0 Months Ended		1 Months Ended				12 Months Ended					0 Months Ended	1 Months Ended				12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Credit Facility Rates	Nov. 25, 2013 Credit Facility	Sep. 12, 2013 Credit Facility	Feb. 15, 2013 Credit Facility	Dec. 31, 2012 Credit Facility	Dec. 31, 2013 Credit Facility JPMorgan Chase Bank and other ten banks	Dec. 31, 2013 Credit Facility Other ten banks Banks	Dec. 31, 2013 Credit Facility Other lenders	Dec. 31, 2013 Credit Facility Borrowing base utilization equal to 50% or Less	Dec. 31, 2013 Credit Facility Borrowing base utilization greater than 50%	Dec. 31, 2013 Credit Facility On or before September 11, 2013	Dec. 31, 2013 Credit Facility After September 11, 2013 and on or before March 31, 2014	Dec. 31, 2013 Credit Facility After April 1, 2014 and on or before June 30, 2014	Dec. 31, 2013 Credit Facility After June 30, 2014	Dec. 31, 2013 Credit Facility Prime Rate Minimum	Dec. 31, 2013 Credit Facility Prime Rate Maximum	Dec. 31, 2013 Credit Facility Federal funds rate	Dec. 31, 2013 Credit Facility Federal funds rate Minimum	Dec. 31, 2013 Credit Facility Federal funds rate Maximum	Dec. 31, 2013 Credit Facility One-month adjusted LIBO rate for one, two, three or six months	Dec. 31, 2013 Credit Facility One-month adjusted LIBO rate for one, two, three or six months Minimum	Dec. 31, 2013 Credit Facility One-month adjusted LIBO rate for one, two, three or six months Maximum	Dec. 31, 2013 Credit Facility Adjusted LIBO Minimum	Dec. 31, 2013 Credit Facility Adjusted LIBO Maximum	Dec. 31, 2013 7% Senior Subordinated Notes due 2013		Dec. 31, 2012 7% Senior Subordinated Notes due 2013	Feb. 17, 2009 8 1/2% Senior Notes due 2014	Mar. 31, 2013 8 1/2% Senior Notes due 2014	Oct. 31, 2012 8 1/2% Senior Notes due 2014	Dec. 31, 2013 8 1/2% Senior Notes due 2014		Dec. 31, 2012 8 1/2% Senior Notes due 2014	May 22, 2008 7 1/4% Senior Notes due 2019	Jun. 06, 2007 7 1/4% Senior Notes due 2019	Nov. 30, 2013 7 1/4% Senior Notes due 2019	Dec. 31, 2013 7 1/4% Senior Notes due 2019		Dec. 31, 2012 7 1/4% Senior Notes due 2019	Dec. 31, 2013 7 1/4% Senior Notes due 2019 Redemption Period One	Dec. 31, 2013 7 1/4% Senior Notes due 2019 Redemption Period Two	Dec. 31, 2013 7 1/4% Senior Notes due 2019 Redemption Period Three	Dec. 31, 2013 7 1/4% Senior Notes due 2019 Redemption Period Four	Nov. 30, 2013 7 1/4% Senior Notes due 2019 and 7 1/2% Senior Notes due 2020	Sep. 17, 2012 7 1/2% Senior Notes due 2020	Nov. 30, 2013 7 1/2% Senior Notes due 2020	Dec. 31, 2013 7 1/2% Senior Notes due 2020		Dec. 31, 2012 7 1/2% Senior Notes due 2020	Dec. 31, 2013 7 1/2% Senior Notes due 2020 Redemption Period One Equity Offering Net Proceeds	Dec. 31, 2013 7 1/2% Senior Notes due 2020 Redemption Period Two	Dec. 31, 2013 7 1/2% Senior Notes due 2020 Redemption Period Three	Dec. 31, 2013 7 1/2% Senior Notes due 2020 Redemption Period Four	Dec. 31, 2013 7 1/2% Senior Notes due 2020 Redemption Period Five
Debt
Credit Facility		$ 65,000,000		$ 0				$ 65,000,000
Interest rate (as a percent)																														7.00%		8.50%	8.50%			8.50%			7.25%	7.25%		7.25%							7.50%	7.50%		7.50%
Total debt
Debt, Principal	800,001,000	1,865,012,000																										0	[1]	12,000	600,000,000			0	[2]	300,000,000	250,000,000	750,000,000		577,914,000	[3]	1,000,000,000						500,000,000		222,087,000	[4]	500,000,000
Debt, Unamortized Premium (Discount)	178,000	(2,912,000)		0				0																				0	[1]	0				0	[2]	(3,277,000)				178,000	[3]	365,000								0	[4]	0
Total debt	800,179,000	1,862,100,000																										0	[1]	12,000				0	[2]	296,723,000				578,092,000	[3]	1,000,365,000								222,087,000	[4]	500,000,000
Less: current portion of debt
Less: current portion of debt, Principal	0	(12,000)
Less: current portion of debt, Unamortized Premium (Discount)	0	0
Current portion of debt	0	(12,000)
Long-term portion of debt
Long-term portion of debt, Principal	800,001,000	1,865,000,000
Long-term portion of debt, Unamortized Premium (Discount)	178,000	(2,912,000)
Long-term portion of debt	800,179,000	1,862,088,000
Bank Credit Facility
Maximum borrowing capacity				1,500,000,000
Increase in the credit facility's borrowing capacity available subject to the agreement				300,000,000
Maximum borrowing capacity optional expansion				1,800,000,000
Borrowing base under the Credit Facility				400,000,000		700,000,000
Reduction in borrowing base due to the issuance of new senior unsecured notes expressed as a percentage of the stated principal amount of the new notes (as a percent)				25.00%
Fair market value of assets included in borrowing base and are sold in excess of borrowing base in effect (as a percent)				10.00%
Borrowing Base Reduction Due To Sale of Properties					300,000,000		170,000,000
Credit Facility collateral as percentage of present value of estimated proved oil and gas properties and related assets (as a percent)				75.00%
Number of interest rate alternatives				2
Spread on variable rate (as a percent)																		0.50%	1.50%	0.50%	0.50%	1.50%	1.00%	0.50%	1.50%	1.50%	2.50%
Ratio of total debt to EBITDA, numerator														4.50	5.00	4.75	4.50
Ratio of total debt to EBITDA, denominator														1.00	1.00	1.00	1.00
Ratio of total debt outstanding to EBITDA				4.3
Number of lenders										10
Commitment held by lenders (as a percent)									68.00%		32.00%
Commitment held by lenders, maximum (as a percent)											3.30%
Credit Facility, utilization percentage threshold to change commitment fee (as a percent)				50.00%
Credit Facility, commitment fees for unutilized amount (as a percent)												0.35%	0.50%
Credit facility, weighted average interest rate								2.10%
Outstanding letters of credit				2,100,000				1,600,000
Credit facility, unused borrowing amount				397,900,000				1,000,000,000
Senior Notes
Issuance price of senior notes as a percentage of par value (as a percent)																															95.15%						100.25%
Net proceeds from issuance of senior notes after deducting initial purchaser discounts	0	491,250,000	0																												559,800,000						247,200,000	739,200,000										491,250,000
Face amount of senior notes that were redeemed																																300,000,000	300,000,000						422,100,000								700,000,000		277,900,000
Loss on debt extinguishment, net	48,725,000	36,312,000	0																													25,200,000	36,312,000						14,700,000										8,800,000
Senior notes effective interest rate (as a percent)																																								7.24%
Senior notes redemption price as a percentage of par (as a percent)																																107.11%	110.24%						102.77%				103.625%	102.417%	101.208%	100.00%			101.50%				107.50%		103.75%	101.875%	100.00%
Senior notes redemption period start date																																											Jun. 15, 2012	Jun. 15, 2013	Jun. 15, 2014	Jun. 15, 2015							Jan. 01, 2014	Jan. 01, 2014	Sep. 15, 2016	Sep. 15, 2017	Sep. 15, 2018
Senior notes redemption period end date																																											Jun. 14, 2013	Jun. 14, 2014	Jun. 14, 2015	Dec. 31, 2019							Sep. 14, 2015	Sep. 14, 2016	Sep. 14, 2017	Sep. 14, 2018	Dec. 31, 2020
Senior notes redemption variable rate basis of make-whole premium																																																						Treasury Yield
Senior notes redemption basis spread of make-whole premium (as a percent)																																																						0.50%
Percentage of senior notes that may be redeemed with proceeds from certain equity offerings (as a percent)																																																					35.00%
Percentage of senior notes that must remain outstanding (as a percent)																																																					65.00%
Number of days the redemption of senior notes must occur within from the date of the equity offering																																																					120 days
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Principal Maturities
2014	0
2015	0
2016	0
2017	0
2018	0
Thereafter	$ 800,001,000

[1] In June 2013, Forest redeemed the 7% senior subordinated notes due 2013 at their maturity.

[2] In March 2013, Forest redeemed the 8½% senior notes due 2014 at 107.11% of par, recognizing a loss of $25.2 million upon redemption.

[3] In November 2013, Forest redeemed $422.1 million in principal amount of 7¼% senior notes due 2019 at 102.77% of par, recognizing a net loss of $14.7 million upon redemption.

[4] In November 2013, Forest redeemed $277.9 million in principal amount of 7½% senior notes due 2020 at 101.50% of par, recognizing a loss of $8.8 million upon redemption.