Regulatory requirements (Details)	9 Months Ended
	Sep. 30, 2023 USD ($)	Jan. 31, 2022 GBP (£)	Jan. 31, 2022 EUR (€)
Oppenheimer
Regulatory Capital Requirements [Line Items]
Required percentage of net capital to aggregate customer-related debit items (as a percent)	2.00%
Net capital	$ 437,100,000
Aggregate indebtedness (as a percent)	40.26%
Excess capital	$ 415,400,000
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]
Common Equity Tier 1 Ratio (as a percent)	122.00%
Common Equity Tier 1 Ratio Required (as a percent)	56.00%
Tier 1 Capital Ratio Required (as a percent)	75.00%
Total Capital Ratio (as a percent)	167.00%
Total Capital Ratio Required (as a percent)	100.00%
Regulatory capital required to be maintained		£ 750,000	€ 730,000
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained	$ 383,083
Net capital	4,200,000
Excess Liquid Capital under Hong Kong SFC Rules	$ 3,900,000