Selected Quarterly Financial Data (Unaudited) - Summary of the Unaudited Quarterly Results of Operations (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
Quarterly Financial Information Disclosure [Abstract]
Net interest income	$ 51,553	$ 51,431	$ 50,868	$ 49,976	$ 50,075	$ 46,876	$ 46,215	$ 45,626	$ 203,828	$ 188,792	$ 181,351
Provision for loan losses	1,672	2,940	2,804	4,103	3,646	1,424	1,271	1,334	11,519	7,675	3,072
Securities transactions	52	(146)	(65)	100	2,148		5,392	1,729	(59)	9,269	1,641
Noninterest income	27,431	27,927	26,057	25,617	26,473	25,324	28,715	25,296	107,032	105,808	96,413
Noninterest expense	48,189	49,204	47,720	46,291	49,011	46,352	45,429	44,923	191,404	185,715	183,521
Net income	$ 18,620	$ 17,982	$ 17,493	$ 16,579	$ 15,728	$ 15,630	$ 18,553	$ 16,259	$ 70,674	$ 66,170	$ 63,887
Net income per common share:
Basic	$ 1.19	$ 1.15	$ 1.12	$ 1.07	$ 1.00	$ 1.01	$ 1.19	$ 1.05	$ 4.53	$ 4.25	$ 4.14
Diluted	$ 1.16	$ 1.13	$ 1.10	$ 1.05	$ 0.99	$ 0.98	$ 1.17	$ 1.03	$ 4.44	$ 4.17	$ 4.04