Revenue Recognition - Summary of Topic 606 Revenue Items (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Abstract]
Wealth management fees	$ 9,022	$ 8,837	$ 27,794	$ 27,515
Service charges on deposit accounts	11,028	10,535	32,552	30,418
Debit card and ATM fees	4,706	4,248	14,651	12,920
Investment product fees	5,073	5,193	15,170	15,186
Other income:
Merchant processing fees	779	684	2,198	1,914
Gain (loss) on other real estate owned	260	206	981	823
Safe deposit box fees	221	190	849	704
Insurance premiums and commissions	83	170	265	437
Total	$ 31,172	$ 30,063	$ 94,460	$ 89,917