Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for loan losses:
Beginning balance	$ 120,856	$ 114,419
Loans charged-off	(8,063)	(11,074)
Charged-off loans recovered	7,405	8,980
Net (charge-offs) recoveries	(658)	(2,094)
Provision for loan losses	31,661	8,531	$ 11,873
Ending balance	151,859	120,856	114,419
Commercial and Industrial
Allowance for loan losses:
Beginning balance	57,232	50,820
Loans charged-off	(2,515)	(5,421)
Charged-off loans recovered	4,623	4,736
Net (charge-offs) recoveries	2,108	(685)
Provision for loan losses	31,616	7,097
Ending balance	90,956	57,232	50,820
Commercial Real Estate
Allowance for loan losses:
Beginning balance	54,954	55,851
Loans charged-off	(348)	(559)
Charged-off loans recovered	417	1,425
Net (charge-offs) recoveries	69	866
Provision for loan losses	(5,373)	(1,763)
Ending balance	49,650	54,954	55,851
Residential Mortgage
Allowance for loan losses:
Beginning balance	3,605	3,702
Loans charged-off	(223)	(530)
Charged-off loans recovered	272	1,016
Net (charge-offs) recoveries	49	486
Provision for loan losses	1,387	(583)
Ending balance	5,041	3,605	3,702
Consumer
Allowance for loan losses:
Beginning balance	5,065	4,046
Loans charged-off	(4,977)	(4,564)
Charged-off loans recovered	2,093	1,803
Net (charge-offs) recoveries	(2,884)	(2,761)
Provision for loan losses	4,031	3,780
Ending balance	$ 6,212	$ 5,065	$ 4,046