Financial instruments - Notional and Fair Values of TBAs (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Of To Be Announced Securities [Abstract]
FHA loan commitments balance	$ 264.0	$ 304.4
OMHHF had a loan receivable balance (included in other assets)	$ 25.7	$ 22.9

This represents the prior loan commitments that have been funded but not yet been securitized.

No definition available.

Name:	opy_LoanPurchasedUnderCommitmentFromFederalHousingAdministration
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant