Regulatory Requirements - Additional Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 EUR (€)
Oppenheimer
Regulatory Capital Requirements [Line Items]
Required percentage of net capital to aggregate customer-related debit items	$ 0.02
Broker-Dealer, Net Capital	223,400,000
Excess capital	$ 206,700,000
Aggregate indebtedness	26.83%
Freedom
Regulatory Capital Requirements [Line Items]
Broker-Dealer, Net Capital	$ 5,100,000
Freedom maintain net capital equal to the greater	$ 100,000
Aggregate indebtedness	6.67%
Net capital in excess of minimum required	$ 5,000,000
Oppenheimer Europe Ltd
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained | €		€ 730,000
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Net capital	1,900,000
Excess Liquid Capital under Hong Kong SFC Rules	1,500,000
Regulatory capital required to be maintained	$ 400,000
Basel Three New Requirements [Member] | Oppenheimer Europe Ltd
Regulatory Capital Requirements [Line Items]
Common Equity Tier 1 Ratio	21.02%	21.02%
Common Equity Tier 1 Ratio Required	4.50%	4.50%
Tier 1 Capital Ratio	21.02%	21.02%
Tier 1 Capital Ratio Required	6.00%	6.00%
Total Capital Ratio	21.02%	21.02%
Total Capital Ratio Required	8.00%	8.00%