Fair Value Measurements (Details) - EBP 001 - USD ($)	Dec. 31, 2025	Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	$ 793,959,006	$ 687,728,630
Mutual funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	698,086,685	596,635,843
Oppenheimer Holdings Inc. - Common stock
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	38,237,289	36,321,533
Money market funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	57,620,914	54,757,486
Cash surrender value life insurance policies
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	14,118	13,768
Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	793,944,888	687,714,862
Level 1 \| Mutual funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	698,086,685	596,635,843
Level 1 \| Oppenheimer Holdings Inc. - Common stock
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	38,237,289	36,321,533
Level 1 \| Money market funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	57,620,914	54,757,486
Level 1 \| Cash surrender value life insurance policies
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	0	0
Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	14,118	13,768
Level 2 \| Mutual funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	0	0
Level 2 \| Oppenheimer Holdings Inc. - Common stock
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	0	0
Level 2 \| Money market funds
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	0	0
Level 2 \| Cash surrender value life insurance policies
EBP, Investment, Fair Value and NAV [Line Items]
Total investments at fair value	$ 14,118	$ 13,768

Fair value of investment, excluding plan interest in master trust, held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, derivative, investment measured at net asset value per share as practical expedient, and insurance contract not meeting fully-benefit responsive investment criteria.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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