Earnings Per Share - Reconciliation of Numerators and Denominators Used in Computations of Both Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basic earnings (loss) per share computation:
Income (loss) from continuing operations	$ 18,818	$ 20,233	$ 26,519	$ (73,651)	$ 5,704	$ (15,136)	$ (963)	$ (9,792)	$ (8,081)	$ (20,187)	$ 325,359
Average common shares - Basic									93,298,467	93,916,656	93,785,611
Basic earnings (loss) per share from continuing operations (in dollars per share)									$ (0.09)	$ (0.22)	$ 3.47
Diluted earnings (loss) per share computation:
Income (loss) from continuing operations	$ 18,818	$ 20,233	$ 26,519	$ (73,651)	$ 5,704	$ (15,136)	$ (963)	$ (9,792)	$ (8,081)	$ (20,187)	$ 325,359
Stock option conversion									0	0	670,485
Stock units									0	0	340,140
Average common shares - diluted									93,298,467	93,916,656	94,796,236
Diluted earnings (loss) per share from continuing operations (in dollars per share)									$ (0.09)	$ (0.22)	$ 3.43
Common Stock
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded (in shares)									2,933,770	3,840,637	3,554,064
Stock Units
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded (in shares)									340,398	312,971	7,071