Premises, Equipment, and Leases - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) Lease	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Premises Equipment And Lessee Lease [Line Items]
Consolidated premises and equipment depreciation and amortization expenses	$ 56,100	$ 50,800	$ 47,400
Consolidated rental and operating lease expenses			$ 14,800
Option to extend, operating lease, description	leases include one or more options to renew, with renewal terms that can extend the lease term from one month to 40 years or more.
Option to extend, existence, operating lease	true
Number of leases including option to purchase leased property | Lease	0
Right-of-use asset	$ 63,400	$ 66,800
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets	us-gaap:OtherAssets
Lease liability	$ 71,680	$ 73,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilities	us-gaap:OtherLiabilities
Lease expense	$ 12,800	$ 12,300
Lease payments	12,300	12,100
Leased assets obtained in exchange for new operating lease liabilities	$ 7,200	$ 19,200
Weighted average remaining lease term	8 years 2 months 12 days	8 years 7 months 6 days
Weighted average discount rate	2.85%	3.06%
Minimum [Member]
Premises Equipment And Lessee Lease [Line Items]
Remaining lease terms	1 year
Lessee, operating lease, renewal term	1 month
Maximum [Member]
Premises Equipment And Lessee Lease [Line Items]
Remaining lease terms	27 years
Lessee, operating lease, renewal term	40 years