Reconciliation of Net Income and Weighted-Average Shares of Common Stock Outstanding for Purposes of Calculating Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net (loss) income	$ (52,165)	$ 11,228	$ (22,310)	$ 30,157
Denominator:
Weighted average shares outstanding - basic	44,323	44,039	44,275	44,030
Dilutive effect of share-based awards		167		160
Weighted average shares outstanding - diluted	44,323	44,206	44,275	44,190
Earnings per share:
Basic	$ (1.18)	$ 0.25	$ (0.50)	$ 0.68
Diluted	$ (1.18)	$ 0.25	$ (0.50)	$ 0.68