Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Minimum corporation reserves for commercial loan	$ 1.0
Core deposit intangibles amortization period, years	10 years
Qualified affordable housing project investments	$ 59.6	$ 43.7
Qualified affordable housing project investments, unfunded commitments	$ 60.1	57.0
Largest amount recognized in the financial statement of tax benefit threshold, minimum	Greater than 50%
Marketing expense	$ 13.1	$ 12.8	$ 11.5
Restricted Stock Units (RSUs)
Summary Of Significant Accounting Policies [Line Items]
Vesting period of awards issued, years	3 years
Total commercial loans
Summary Of Significant Accounting Policies [Line Items]
Number of days placed on non-accrual	90 days
Installment Loans
Summary Of Significant Accounting Policies [Line Items]
Number of days placed on non-accrual	120 days
Residential Mortgages
Summary Of Significant Accounting Policies [Line Items]
Number of days placed on non-accrual	180 days
Minimum
Summary Of Significant Accounting Policies [Line Items]
Useful life of the asset, years	3 years
Estimated useful life of intangibles, years	8 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Useful life of the asset, years	39 years
Estimated useful life of intangibles, years	13 years