Regulatory requirements (Details)	3 Months Ended
	Mar. 31, 2026 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	$ 437,200,000
Aggregate indebtedness (as a percent)	26.28%
Excess capital	$ 403,900,000
Oppenheimer Europe Ltd | Basel Three New Requirements
Regulatory Capital Requirements [Line Items]
Common Equity Tier 1 ratio (as a percent)	157.00%
Common equity tier 1 ratio required (as a percent)	56.00%
Tier 1 capital ratio (as a percent)	157.00%
Tier 1 capital ratio required (as a percent)	75.00%
Total capital ratio (as a percent)	209.00%
Total capital ratio required (as a percent)	100.00%
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Net capital	$ 3,500,000
Excess liquid capital under hong kong SFC rules	3,100,000
Regulatory capital required to be maintained	$ 382,612