| Cover | Jul. 31, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 31, 2020 |
| Entity Registrant Name | OPPENHEIMER HOLDINGS INC. |
| Entity Central Index Key | 0000791963 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 1-12043 |
| Entity Tax Identification Number | 98-0080034 |
| Entity Address, Address Line One | 85 Broad Street |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10004 |
| City Area Code | 212 |
| Local Phone Number | 668-8000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | OPY |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
