Earnings per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 12,533	$ 12,199	$ 9,405	$ 10,674	$ 11,422	$ 12,694	$ 11,366	$ 8,336	$ 44,811	$ 43,818	$ 26,108
Average number of common shares outstanding									22,814	22,750	17,716
Effect of dilutive stock options									273	248	207
Average number of common shares outstanding used to calculate diluted earnings per share									23,087	22,998	17,923