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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Basic earnings (loss) per share computation:
Income (loss) from continuing operations	$ 5,704	$ (15,136)	$ (963)	$ (9,792)	$ (37,362)	$ 415,518	$ (32,057)	$ (20,740)	$ (20,187)		$ 325,359		$ 23,815
Average common shares - Basic									93,916,656	[1]	93,785,611	[1]	92,375,378	[1]
Basic earnings (loss) per share from continuing operations									$ (0.22)	[1]	$ 3.47	[1]	$ 0.26	[1]
Diluted earnings (loss) per share computation:
Income (loss) from continuing operations	$ 5,704	$ (15,136)	$ (963)	$ (9,792)	$ (37,362)	$ 415,518	$ (32,057)	$ (20,740)	$ (20,187)		$ 325,359		$ 23,815
Stock option conversion									0		670,485		245,911
Stock units									0		340,140		444,623
Average common shares - diluted									93,916,656	[1]	94,796,236	[1]	93,065,912	[1]
Diluted earnings (loss) per share from continuing operations									$ (0.22)	[1]	$ 3.43	[1]	$ 0.26	[1]
Common Stock
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded									3,840,637		3,554,064		7,099,437
Stock Units
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded									312,971		7,071		8,192

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