SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Earnings (Loss) per Share) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share
Net earnings (loss)	$ (286,533)	[1]	$ (458,552)	[1]	$ (511,173)	[1]	$ (32,673)	[1]	$ 19,467	[1]	$ 87,718	[1]	$ 38,974	[1]	$ (3,330)	[1]	$ (1,288,931)	$ 142,829	$ 227,521
Net earnings attributable to noncontrolling interest																	0	(4,987)	0
Net earnings attributable to participating securities																	0	(2,858)	(4,482)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	(1,288,931)	134,984	223,039
Adjustment for liability classified stock-based compensation awards																	0	(707)	500
Net earnings (loss) for diluted earnings (loss) per share																	(1,288,931)	134,277	223,539
Weighted Average Number of Shares Outstanding Reconciliation
Weighted average common shares outstanding during the period for basic earnings (loss) per share (in shares)																	114,958	111,690	110,809
Dilutive effects of potential common shares (in shares)																	0	1,178	689
Weighted average common shares outstanding during the period, including the effects of dilutive potential common shares, for diluted earnings (loss) per share (in shares)																	114,958	112,868	111,498
Continuing Operations
Earnings Per Share
Net earnings (loss)																	(1,288,931)	98,260	189,662
Net earnings attributable to noncontrolling interest																	0	0	0
Net earnings attributable to participating securities																	0	(2,037)	(3,736)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	(1,288,931)	96,223	185,926
Adjustment for liability classified stock-based compensation awards																	0	0	0
Net earnings (loss) for diluted earnings (loss) per share																	(1,288,931)	96,223	185,926
Discontinued Operations
Earnings Per Share
Net earnings (loss)																	0	44,569	37,859
Net earnings attributable to noncontrolling interest																	0	(4,987)	0
Net earnings attributable to participating securities																	0	(821)	(746)
Net earnings (loss) attributable to common stock for basic earnings (loss) per share																	0	38,761	37,113
Adjustment for liability classified stock-based compensation awards																	0	(707)	500
Net earnings (loss) for diluted earnings (loss) per share																	$ 0	$ 38,054	$ 37,613

[1] Earnings (loss) before income taxes, net earnings (loss), and net earnings (loss) attributable to Forest Oil Corporation common shareholders have been impacted by non-cash ceiling test write-downs in every quarter of 2012 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.