Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 21,515	$ 20,609	$ 21,796	$ 19,802	$ 21,219	$ 19,032	$ 16,351	$ 17,029	$ 83,722	$ 73,631	$ 70,534
Basic weighted average common shares outstanding									62,945,669	60,388,398	57,236,909
Dilutive shares									169,049	173,672	124,534
Diluted weighted average common shares outstanding									63,114,718	60,562,070	57,361,443
Earnings per share:
Basic (in dollars per share)	$ 0.34	$ 0.33	$ 0.35	$ 0.32	$ 0.34	$ 0.30	$ 0.28	$ 0.30	$ 1.33	$ 1.22	$ 1.23
Diluted (in dollars per share)	$ 0.34	$ 0.33	$ 0.35	$ 0.32	$ 0.34	$ 0.30	$ 0.28	$ 0.30	$ 1.33	$ 1.22	$ 1.23
Anti-dilutive stock options and awards excluded from computation of earnings per share (in shares)									469,018	988,931	659,531