Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended
	Jan. 01, 2020 USD ($)	Mar. 31, 2020 USD ($) Portfolio	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Non-accrual status period		90 days
Loans returned to accrual status, performance period		6 months
Number of categories of loan portfolio | Portfolio		3
Minimum loan balance individually tested for impairment		$ 1,000,000
Recognition on retained earnings		(26,591,000)
Allowance for credit loss for held-to-maturity		236,000
ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Recognition on retained earnings	$ 41,400,000	41,442,000
Adjustment for loan credit losses	6,700,000
Adjustment for loan commitments	3,000,000.0
Recognition after tax for retained earnings	$ 26,600,000
Regulatory capital impact period	1 year
Allowance for credit loss for held-to-maturity	$ 200,000	$ 236,000	$ 229,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Forecast period to measure expected credit losses on loan portfolio		1 year
Model reversion period to measure expected credit losses on loan portfolio		1 year
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Forecast period to measure expected credit losses on loan portfolio		2 years
Model reversion period to measure expected credit losses on loan portfolio		3 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
Home Equity [Member] | ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Recognition on retained earnings		$ (3,936,000)
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