Regulatory requirements (Details)	12 Months Ended
	Dec. 31, 2023 USD ($)	Jan. 31, 2022 GBP (£)	Jan. 31, 2022 EUR (€)
Regulatory Capital Requirements [Line Items]
Minimum capital required	$ 4,150,000
Oppenheimer
Regulatory Capital Requirements [Line Items]
Required percentage of net capital to aggregate customer-related debit items (as a percent)	2.00%
Net capital	$ 453,600,000
Aggregate indebtedness (as a percent)	48.86%
Excess capital	$ 435,000,000.0
Freedom
Regulatory Capital Requirements [Line Items]
Net capital	$ 4,100,000
Aggregate indebtedness (as a percent)	6.67%
Freedom maintain net capital equal to the greater	$ 100,000
Net capital in excess of minimum required	$ 4,000,000
Oppenheimer Europe Ltd
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained		£ 750,000	€ 730,000
Oppenheimer Europe Ltd | Basel Three New Requirements
Regulatory Capital Requirements [Line Items]
Common Equity Tier 1 ratio (as a percent)	134.00%
Common Equity Tier 1 ratio required (as a percent)	56.00%
Tier 1 Capital ratio (as a percent)	134.00%
Tier 1 Capital ratio required (as a percent)	75.00%
Total Capital ratio (as a percent)	182.00%
Total Capital ratio required (as a percent)	100.00%
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained	$ 384,120
Regulatory capital	4,000,000
Excess Liquid Capital under Hong Kong SFC rules	$ 3,600,000