Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Branch	Jan. 01, 2019 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2000 Branch
Significant Accounting Policies [Line Items]
Secured borrowings maturity period under repurchase agreements	1 year
Personal loans charged off period no later than period	180 days
Percentage of excess loan balance for watch category	90.00%
Impaired loans measurement	Impaired loans measured individually for impairment generally include (1) any loan risk rated Special Mention or worse where the borrower has filed for bankruptcy; (2) all loans risk rated Substandard or worse with balances of $400 thousand or more; and (3) all loans classified as TDRs.
Loan Receivables	$ 902,345,000		$ 766,296,000
Number of branches purchased during the years 1994 through 2000 | Branch	19			5
Deferred tax assets valuation allowance	$ 0
ASU 2016-02 | Subsequent Event
Significant Accounting Policies [Line Items]
Operating lease right of use asset		$ 3,500,000
Operating lease liability		$ 3,900,000
Core Deposits
Significant Accounting Policies [Line Items]
Amortization of intangible assets, estimated useful life	92 months
Substandard
Significant Accounting Policies [Line Items]
Loan Receivables	$ 9,587,000		$ 11,371,000
Minimum
Significant Accounting Policies [Line Items]
Number of days past due for a loan to remain on accrual status	90 days
Minimum | Building
Significant Accounting Policies [Line Items]
Estimated useful lives	10 years
Minimum | Furniture and Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Minimum | Substandard
Significant Accounting Policies [Line Items]
Loan Receivables	$ 400,000
Maximum | Building
Significant Accounting Policies [Line Items]
Estimated useful lives	40 years
Maximum | Furniture and Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives	10 years
Maximum | Substandard
Significant Accounting Policies [Line Items]
Loan Receivables	$ 400,000