Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 23,211	$ 16,170	$ 15,029	$ 13,910	$ 2,989	$ 11,897	$ 13,589	$ 12,079	$ 68,320	$ 40,554	$ 44,811
Average number of common shares outstanding									26,593	22,912	22,814
Effect of dilutive stock options and restricted stock									287	338	273
Average number of common shares outstanding used to calculate diluted earnings per share									26,880	23,250	23,087
Options excluded from diluted earnings per share because the effect of these options was antidilutive									10,056		13,825