SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Earnings (Loss) per Share) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share
Net earnings (loss)	$ 106,219	[1]	$ 2,214	[1]	$ 33,439	[1]	$ (67,948)	[1]	$ (286,533)	[1]	$ (458,552)	[1]	$ (511,173)	[1]	$ (32,673)	[1]	$ 73,924	$ (1,288,931)	$ 142,829
Less: net earnings attributable to noncontrolling interest																	0	0	(4,987)
Less: net earnings attributable to participating securities																	(2,099)	0	(2,858)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	71,825	(1,288,931)	134,984
Adjustment for liability classified stock-based compensation awards																	0	0	(707)
Net earnings (loss) for diluted earnings (loss) per share																	71,825	(1,288,931)	134,277
Weighted Average Number of Shares Outstanding Reconciliation
Weighted average common shares outstanding during the period for basic earnings (loss) per share (in shares)																	116,125	114,958	111,690
Dilutive effects of potential common shares (in shares)																	0	0	1,178
Weighted average common shares outstanding during the period, including the effects of dilutive potential common shares, for diluted earnings (loss) per share (in shares)																	116,125	114,958	112,868
Continuing Operations
Earnings Per Share
Net earnings (loss)																	73,924	(1,288,931)	98,260
Less: net earnings attributable to noncontrolling interest																	0	0	0
Less: net earnings attributable to participating securities																	(2,099)	0	(2,037)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	71,825	(1,288,931)	96,223
Adjustment for liability classified stock-based compensation awards																	0	0	0
Net earnings (loss) for diluted earnings (loss) per share																	71,825	(1,288,931)	96,223
Discontinued Operations
Earnings Per Share
Net earnings (loss)																	0	0	44,569
Less: net earnings attributable to noncontrolling interest																	0	0	(4,987)
Less: net earnings attributable to participating securities																	0	0	(821)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	0	0	38,761
Adjustment for liability classified stock-based compensation awards																	0	0	(707)
Net earnings (loss) for diluted earnings (loss) per share																	$ 0	$ 0	$ 38,054

[1] Earnings (loss) before income taxes and net earnings (loss) have been impacted by non-cash ceiling test write-downs in every quarter of 2012 and the fourth quarter of 2013, as discussed in Note 1, and are also subject to large fluctuations due to Forest’s election not to use cash flow hedge accounting for derivative instruments as discussed in Note 9. Also impacting the fourth quarter of 2013 is a $193.0 million net gain on the Panhandle divestiture, as discussed in Note 2.