Loans and Allowance for Loan Losses - Summary Composition of the Allowance for Loan Losses by Type (Detail)	Jun. 30, 2018 USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 21,425,000
Percentage of Allowance	100.00%
Allowance as a Percent of Loan Category	$ 0.0186
Recreation [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 1,963,000
Percentage of Allowance	9.00%
Allowance as a Percent of Loan Category	$ 0.0033
Home Improvement [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 555,000
Percentage of Allowance	3.00%
Allowance as a Percent of Loan Category	$ 0.0028
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 175,000
Percentage of Allowance	1.00%
Allowance as a Percent of Loan Category	$ 0.0022
Medallion [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Amount	$ 18,732,000
Percentage of Allowance	87.00%
Allowance as a Percent of Loan Category	$ 0.0677