Reconciliation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 13,154	$ 29,217	$ 26,390	$ 53,111
Weighted average shares outstanding - basic	33,171	33,552	33,165	33,560
Dilutive effect of restricted stock	284	163	307	90
Weighted average shares outstanding - diluted	33,455	33,715	33,472	33,650
Earnings per share - basic	$ 0.40	$ 0.87	$ 0.80	$ 1.58
Earnings per share - diluted	$ 0.39	$ 0.87	$ 0.79	$ 1.58