Note 9 - Interest on Deposits - Interest on Deposits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Savings and other deposits	$ 1,465	$ 896
Time deposits over $250,000	68	74
Other time deposits	73	95
	$ 1,606	$ 1,065

Represents the interest expense incurred on savings and other deposits.

No definition available.

Name:	ovly_InterestExpenseSavingsDepositsAndOtherDeposits
Namespace Prefix:	ovly_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Interest expense incurred on time deposits, including certificates of deposits, more than $250,000 in domestic offices.

+ References

No definition available.

+ Details

Name:	ovly_InterestExpenseTimeDepositsMoreThan250000
Namespace Prefix:	ovly_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate amount of interest expense on all deposits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.6)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

+ Details

Name:	us-gaap_InterestExpenseDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest expense on domestic time deposit liabilities other than certificates of liabilities.

+ References

+ Details

Name:	us-gaap_InterestExpenseDomesticDepositLiabilitiesOtherTimeDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration