Selected Financial Data - Summary of Selected Financial Data (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	$ 53,353	$ 53,669	$ 52,611	$ 43,916	$ 41,381	$ 40,605	$ 39,872	$ 38,665	$ 203,548	$ 160,523	$ 153,756
Interest expense	4,468	4,073	3,800	3,657	3,315	3,076	3,017	3,074	15,997	12,481	14,563
Provision for loan losses	3,915	3,206	2,059	1,207	1,106	1,454	(1,134)	289	10,388	1,715	8,311
Net Interest Income After Provision for Loan Losses	44,970	46,390	46,752	39,052	36,960	36,075	37,989	35,302	177,163	146,327	130,882
Security gains, net	0	0	(34)	0	0	0	40	1
Noninterest income	13,084	12,481	13,417	12,084	11,220	11,931	11,731	11,415	51,033	46,338	51,527
Noninterest expense	33,817	33,829	35,449	33,621	29,720	28,440	30,165	28,914	136,717	117,240	117,392
Income before taxes	24,237	25,042	24,686	17,515	18,460	19,566	19,595	17,804
Provision for income taxes	6,814	6,407	6,498	4,680	3,963	4,906	4,875	3,771	24,398	17,515	14,478
Net Income Available to Common Shareholders	$ 17,423	$ 18,635	$ 18,188	$ 12,835	$ 14,497	$ 14,660	$ 14,720	$ 14,033	$ 66,801	$ 57,745	$ 50,392
Common earnings per share-diluted (in USD per share)	$ 0.50	$ 0.54	$ 0.52	$ 0.41	$ 0.49	$ 0.49	$ 0.49	$ 0.47	$ 1.98	$ 1.95	$ 1.70
Dividends declared per common share (in USD per share)	0.19	0.18	0.18	0.18	0.18	0.17	0.17	0.16	$ 0.73	$ 0.68	$ 0.61
Common book value (in USD per share)	$ 22.76	$ 22.63	$ 22.15	$ 21.91	$ 20.42	$ 20.33	$ 20.04	$ 19.64