Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Branch Property
Summary Of Significant Accounting Policies [Line Items]
Number of branches | Branch	236
Number of ATM | Property	227
Wholly-owned trust subsidiaries | Property	13
Held for sale securities, percentage of purchase price as condition for sale	15.00%
Non-accrual status period	90 days
Loans returned to accrual status, performance period	6 months
Minimum loan balance individually tested for impairment | $	$ 1,000,000
Indefinite - lived intangible assets | $	$ 0
Period of interest rate lock commitments	60 days
Land Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life	15 years
Consumer Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value	120 days
Home Equity [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value	180 days
Residential Real Estate Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value	180 days
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of voting interest	50.00%
Weighted-average estimated useful lives	10 years
Non-compete agreements, amortization period	1 year
Minimum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life	3 years
Minimum [Member] | Building and Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life	15 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Weighted-average estimated useful lives	16 years
Non-compete agreements, amortization period	4 years
Maximum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life	10 years
Maximum [Member] | Building and Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life	39 years