Earnings per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 25,874	$ 18,119	$ 2,085	$ 838	$ 15,510	$ 17,662	$ 16,468	$ 16,079	$ 46,916	$ 65,719	$ 50,543
Net income allocated to unvested restricted stock awards									(69)	(236)	(333)
Net income allocated to common shares									$ 46,847	$ 65,483	$ 50,210
Weighted average shares outstanding									29,244	29,300	29,370
Average unvested restricted stock awards									(46)	(107)	(193)
Denominator for basic earnings per share—weighted-average shares outstanding	29,237	29,189	29,149	29,218	29,232	29,211	29,181	29,146	29,198	29,193	29,177
Effect of dilutive securities—employee stock options and restricted stock units									70	68	82
Denominator for diluted earnings per share—adjusted weighted-average shares outstanding	29,309	29,217	29,164	29,283	29,313	29,285	29,243	29,205	29,268	29,261	29,259
Basic earnings per share	$ 0.88	$ 0.62	$ 0.07	$ 0.03	$ 0.53	$ 0.60	$ 0.56	$ 0.55	$ 1.60	$ 2.24	$ 1.72
Diluted earnings per share	$ 0.88	$ 0.62	$ 0.07	$ 0.03	$ 0.53	$ 0.60	$ 0.56	$ 0.55	$ 1.60	$ 2.24	$ 1.72
Average anti-dilutive options and restricted stock units excluded from computation of diluted earnings per share									491	325	319