Note 5 - Financial Instruments and Fair Value Measurements (Details Textual)	Mar. 31, 2026
Measurement Input, Combination of Appraisals, Internally Determined Adjustments to Loan Value, and Customized Discounts [Member] \| Valuation, Market Approach [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Nonrecurring [Member]
Individual Evaluated Loans, Measurement Input	0.034

Value of input used to measure individual evaluated loans.

No definition available.

Name:	ovly_IndividualEvaluatedLoansMeasurementInput
Namespace Prefix:	ovly_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant