Commercial Mortgage Banking - Additional Information (Narrative) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Servicing Liability at Amortized Cost [Line Items]
Company owned OMHHF	83.68%
Prepayment costs	$ 9,800,000opy_PrepaymentPenaltyCharges	$ 14,500,000opy_PrepaymentPenaltyCharges	$ 7,400,000opy_PrepaymentPenaltyCharges
Custodial escrow accounts	285,500,000us-gaap_EscrowDeposit	251,400,000us-gaap_EscrowDeposit
Uninsured balance relation to escrow accounts	165,000,000us-gaap_CashUninsuredAmount
Carrying value of loan servicing rights	30,140,000us-gaap_ServicingAssetAtAmortizedValue	28,879,000us-gaap_ServicingAssetAtAmortizedValue	26,983,000us-gaap_ServicingAssetAtAmortizedValue
Servicing rights are amortized using straight-line method	10 years
Mortgage Servicing Rights
Servicing Liability at Amortized Cost [Line Items]
Fair value of servicing rights	42,300,000	40,100,000
Carrying value of loan servicing rights	$ 30,100,000	$ 28,900,000
OMHHF
Servicing Liability at Amortized Cost [Line Items]
Non-controlling interest	16.32%
Number of related party	1

Percentage owned by non-controlling interest.

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Number of related party.

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- Definition

Prepayment penalty charges.

+ References

No definition available.

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- Definition

The amount of cash as of the balance sheet date that is not insured by the Federal Deposit Insurance Corporation.

+ References

No definition available.

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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10)

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7524895&loc=d3e120260-111741

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 860

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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-Publisher FASB

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- Definition

Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

+ References

No definition available.

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