Quarterly Financial Results (Unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 41,074	$ 40,317	$ 38,849	$ 38,072	$ 37,975	$ 37,150	$ 36,991	$ 36,250	$ 158,312	$ 148,366	$ 149,347
Interest expense	5,297	5,201	4,916	4,699	4,748	4,730	4,682	4,658	20,113	18,818	19,433
Net interest income	35,777	35,116	33,933	33,373	33,227	32,420	32,309	31,592	138,199	129,548	129,914
Provision (credit)	1,850	1,706	1,218	597	853	(192)	158	(982)	5,371	(163)	(1,084)
Non-interest income	12,243	12,390	12,109	13,159	11,338	12,590	11,694	11,249	49,901	46,871	47,511
Non-interest Expense	26,996	29,630	29,477	29,244	30,478	28,632	34,141	27,549	115,347	120,800	111,524
Income before income taxes	19,174	16,170	15,347	16,691	13,234	16,570	9,704	16,274	67,382	55,782	66,985
Income tax expense	6,372	5,175	5,014	5,466	4,086	5,428	2,722	5,346	22,027	17,582	22,563
Net income	$ 12,802	$ 10,995	$ 10,333	$ 11,225	$ 9,148	$ 11,142	$ 6,982	$ 10,928	$ 45,355	$ 38,200	$ 44,422
Earnings Per Share, Basic, Total	$ 0.53	$ 0.45	$ 0.42	$ 0.45	$ 0.37	$ 0.44	$ 0.28	$ 0.44	$ 1.84	$ 1.53	$ 1.78
Earnings Per Share, Diluted, Total	$ 0.52	$ 0.45	$ 0.42	$ 0.45	$ 0.36	$ 0.44	$ 0.28	$ 0.43	$ 1.84	$ 1.52	$ 1.77