Earnings (Loss) 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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic earnings (loss) per share computation:
Income (loss) from continuing operations	$ 49,507	$ (9,973)	$ 17,647	$ (9,759)	$ 33,519	$ 14,526	$ 33,371	$ 39,201	$ 47,422	$ 120,617	$ (8,081)
Average common shares - basic (shares)									90,899,284	90,933,886	93,298,467
Basic earnings (loss) per share from continuing operations (USD per share)									$ 0.52	$ 1.33	$ (0.09)
Diluted earnings (loss) per share computation:
Income (loss) from continuing operations	$ 49,507	$ (9,973)	$ 17,647	$ (9,759)	$ 33,519	$ 14,526	$ 33,371	$ 39,201	$ 47,422	$ 120,617	$ (8,081)
Stock option conversion (shares)									119,284	246,116	0
RSUs and PSUs (shares)									255,426	330,481	0
Average common shares - diluted (shares)									91,273,994	91,510,483	93,298,467
Diluted earnings (loss) per share from continuing operations (USD per share)									$ 0.52	$ 1.32	$ (0.09)
Common Stock
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded (shares)									880,541	1,262,158	2,933,770
Stock Units
Diluted earnings (loss) per share computation:
Anti-dilutive options excluded (shares)									442,047	0	340,398