Income (Loss) Per Common Share - Computations of Basic and Diluted (Loss) Income per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
(Loss) income as reported	$ (53,836)		$ 34,755		$ (39,960)		$ 61,015
Participating basic earnings (a)	(119)	[1]	(613)	[1]	(348)	[1]	(1,096)	[1]
Basic (loss) income attributed to common shareholders	(53,955)		34,142		(40,308)		59,919
Reallocation of participating earnings (a)			3	[1]			5	[1]
Diluted (loss) income attributed to common shareholders	(53,955)		34,145		(40,308)		59,924
Basic	$ (0.34)		$ 0.22		$ (0.25)		$ 0.38
Diluted	$ (0.34)		$ 0.21		$ (0.25)		$ 0.38
Continuing Operations [Member]
(Loss) income as reported	(53,836)		33,186		(39,960)		45,531
Participating basic earnings (a)	(119)	[1]	(585)	[1]	(348)	[1]	(818)	[1]
Basic (loss) income attributed to common shareholders	(53,955)		32,601		(40,308)		44,713
Reallocation of participating earnings (a)			3	[1]			3	[1]
Diluted (loss) income attributed to common shareholders	(53,955)		32,604		(40,308)		44,716
Basic	$ (0.34)		$ 0.21		$ (0.25)		$ 0.28
Diluted	$ (0.34)		$ 0.20		$ (0.25)		$ 0.28
Discontinued Operations [Member]
(Loss) income as reported			1,569				15,484
Participating basic earnings (a)		[1]	(28)	[1]		[1]	(278)	[1]
Basic (loss) income attributed to common shareholders			1,541				15,206
Reallocation of participating earnings (a)		[1]				[1]	2	[1]
Diluted (loss) income attributed to common shareholders			$ 1,541				$ 15,208
Basic			$ 0.01				$ 0.10
Diluted			$ 0.01				$ 0.10

[1] Restricted Stock Awards represent participating securities because they participate in nonforfeitable dividends or distributions with common equity owners. Income allocable to participating securities represents the distributed and undistributed earnings attributable to the participating securities. Participating securities, however, do not participate in undistributed net losses.