Earnings Per Common Share - Summary of Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ 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
Numerator for both basic and diluted earnings per common share:
Net income	$ 24,218	$ 17,435	$ 22,109	$ 22,874	$ 23,002	$ 22,248	$ 21,633	$ 13,887	$ 86,635	$ 80,762	$ 69,974
Denominator:
Total average basic common shares outstanding									40,100,320	37,488,331	29,249,499
Effect of dilutive stock options and warrant									26,756	58,796	84,377
Total diluted average common shares outstanding									40,127,076	37,547,127	29,333,876
Earnings per common share - basic	$ 0.55	$ 0.44	$ 0.58	$ 0.60	$ 0.60	$ 0.58	$ 0.56	$ 0.40	$ 2.16	$ 2.15	$ 2.39
Earnings per common share - diluted	$ 0.55	$ 0.44	$ 0.58	$ 0.60	$ 0.60	$ 0.58	$ 0.56	$ 0.40	$ 2.16	$ 2.15	$ 2.39