Regulatory requirements (Details)	9 Months Ended
	Sep. 30, 2025 USD ($)
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained	$ 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	$ 383,000,000.0
Aggregate indebtedness (as a percent)	24.43%
Excess capital	$ 351,700,000
Freedom
Regulatory Capital Requirements [Line Items]
Net capital	$ 3,400,000
Aggregate indebtedness (as a percent)	6.67%
Freedom maintain net capital equal to the greater	$ 100,000
Net capital in excess of minimum required	$ 3,300,000
Oppenheimer Europe Ltd
Regulatory Capital Requirements [Line Items]
Common equity tier 1 ratio (as a percent)	130.00%
Common equity tier 1 ratio required (as a percent)	56.00%
Tier 1 capital ratio (as a percent)	1.30
Tier 1 capital ratio required (as a percent)	75.00%
Total capital ratio (as a percent)	174.00%
Total capital ratio required (as a percent)	100.00%
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Net capital	$ 1,500,000
Excess liquid capital under hong kong SFC rules	1,100,000
Regulatory capital required to be maintained	$ 385,582