Reconciliation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 22,051	$ 9,542	$ 38,218	$ 19,876
Weighted average shares outstanding - basic	33,389	33,220	33,382	33,213
Dilutive effect of stock options and restricted stock	173	42	138	105
Weighted average shares outstanding - diluted	33,562	33,262	33,520	33,318
Earnings per share - basic	$ 0.66	$ 0.29	$ 1.14	$ 0.60
Earnings per share - diluted	$ 0.66	$ 0.29	$ 1.14	$ 0.60