Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 22,890	$ 23,395	$ 23,061	$ 22,726	$ 23,211	$ 16,170	$ 15,029	$ 13,910	$ 92,072	$ 68,320	$ 40,554
Average number of common shares outstanding (in shares)									30,478	26,593	22,912
Effect of dilutive stock options and restricted stock (in shares)									167	287	338
Average number of common shares outstanding used to calculate diluted earnings per share (in shares)									30,645	26,880	23,250
Options excluded from diluted earnings per share because the effect of these options was antidilutive (in shares)									0	10,056	0