Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Office Factor Region Fee RevenueCategory Contract	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of offices | Office	193
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program	100.00%
Number of days to pass to be classified as past due LHFI	30 days
Balance of commercial nonaccrual loans identified for impairment analysis, minimum	$ 500,000
Components in allowance for loan losses methodology | Factor	3
Key market regions | Region	5
Finite-lived intangible assets, average useful life	20 years
Securities with limited marketability	$ 31,900,000	$ 32,200,000
Number of types of interchange fees | Fee	2
Other real estate sales, net (losses) gains	$ (291,000)	700,000	$ 2,087,000
Number of trust management revenue categories | RevenueCategory	5
Time period between service obligation completed and payment received from trust customer	30 days
Operating lease right-of-use assets	$ 31,182,000			$ 33,900,000
Operating lease liabilities	32,354,000			34,900,000
Finance lease right-of-use assets, net of accumulated depreciation	9,326,000	0		11,200,000
Finance lease liabilities	$ 9,520,000			$ 11,200,000
Percentage of right-of-use assets on total assets				0.30%
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Summary Of Significant Accounting Policies [Line Items]
Description of variable rate basis for derivative	three-month LIBOR
Period for which cash flow hedges will be used to hedge quarterly interest payments	5 years
Derivative inception date	Dec. 31, 2014
Derivative maturity date	Dec. 31, 2019
Accumulated net after-tax amount related to effective cash flow hedge	$ 0	$ 469,000
Fisher Brown Bottrell Insurance, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of general categories of insurance contracts | Contract	4
Credit Card Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days past due loans are to be charged-off	180 days
Commercial Credits [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days past due for loan to be classified as nonaccrual	90 days
Non-Business Purpose Credits [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days past due for loan to be classified as nonaccrual	120 days
Number of days past due loans are to be charged-off	120 days
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days mortgage LHFS are retained on balance sheet	30 days
Minimum [Member] | ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected increase in allowance for loan losses	$ 10,000,000.0
Minimum [Member] | Fisher Brown Bottrell Insurance, Inc. [Member] | Personal Insurance Contracts [Member]
Summary Of Significant Accounting Policies [Line Items]
Insurance contracts payment received period	30 days
Minimum [Member] | Fisher Brown Bottrell Insurance, Inc. [Member] | Employee Benefits Insurance Contracts [Member]
Summary Of Significant Accounting Policies [Line Items]
Insurance contracts payment received period	60 days
Minimum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days mortgage LHFS are retained on balance sheet	45 days
Maximum [Member] | ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected increase in allowance for loan losses	$ 35,000,000.0
Maximum [Member] | Fisher Brown Bottrell Insurance, Inc. [Member] | Personal Insurance Contracts [Member]
Summary Of Significant Accounting Policies [Line Items]
Insurance contracts payment received period	60 days
Maximum [Member] | Fisher Brown Bottrell Insurance, Inc. [Member] | Employee Benefits Insurance Contracts [Member]
Summary Of Significant Accounting Policies [Line Items]
Insurance contracts payment received period	90 days
Maximum [Member] | Buildings [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	39 years
Maximum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	10 years
Maximum [Member] | 1-4 Family Residential Real Estate [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days past due loans are to be charged-off	180 days