Earnings Per Share - Reconciliation of Numerators and Denominators Used in Computations of Both Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, 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
Basic earnings (loss) per share computation:
Income (loss) from continuing operations	$ (37,362)	$ 415,518	$ (32,057)	$ (20,740)	$ 7,762	$ (2,192)	$ 19,603	$ (1,358)	$ 325,359		$ 23,815		$ (1,728,282)
Average common shares									93,785,611	[1]	92,375,378	[1]	91,694,110	[1]
Basic earnings (loss) per share from continuing operations									$ 3.47	[1]	$ 0.26	[1]	$ (18.85)	[1]
Diluted earnings (loss) per share computation:
Income (loss) from continuing operations	$ (37,362)	$ 415,518	$ (32,057)	$ (20,740)	$ 7,762	$ (2,192)	$ 19,603	$ (1,358)	$ 325,359		$ 23,815		$ (1,728,282)
Average common shares - basic									93,785,611	[1]	92,375,378	[1]	91,694,110	[1]
Stock option conversion									670,485	[2]	245,911	[2]
Stock units									340,140	[3]	444,623	[3]
Average common shares - diluted									94,796,236	[1]	93,065,912	[1]	91,694,110	[1]
Diluted earnings (loss) per share from continuing operations									$ 3.43	[1]	$ 0.26	[1]	$ (18.85)	[1]

[1] Basic and diluted earnings (loss) per common share and average basic and diluted shares outstanding for the years ended December 31, 2012 and 2011 have been adjusted retroactively to reflect a 1-for-2 reverse stock split effected August 26, 2013.

[2] Anti-dilutive options excluded 3,554,064 7,099,437 10,381,935

[3] Anti-dilutive stock units excluded 7,071 8,192 1,249,885