Earnings per Share - Computation of Earnings Per Share (Detail) - USD ($) 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 [Abstract]
Net income	$ 23,657	$ 17,606	$ 7,430	$ 16,121	$ 22,890	$ 23,395	$ 23,061	$ 22,726	$ 64,814	$ 92,072	$ 68,320
Average number of common shares outstanding (in shares)									29,917	30,478	26,593
Effect of dilutive stock options and restricted stock (in shares)									111	167	287
Average number of common shares outstanding used to calculate diluted earnings per share (in shares)									30,028	30,645	26,880
Options excluded from diluted earnings per share because the effect of these options was antidilutive (in shares)									0	0	10,056