Income Taxes - Additional Information (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 113,000	$ 231,000
Profit (loss) before income taxes for foreign operations	$ (4,000,000)	$ (8,500,000)	$ (965,000)
Effective Income Tax Rate Reconciliation, Percent	35.60%	(10.80%)	56.00%
Impact of the TCJA Tax Reform, Net After Tax Benefit		$ 9,000,000
Effective Income Tax Reconciliation, impact of the TCJA Tax Reform	$ 0	9,013,000	$ 0
Impact of the TCJA Tax Reform, adjustment related to re-measurement of deferred tax liabilities		29,000,000
Impact of the TCJA Tax Reform, adjustment related to re-measurement of deferred tax assets		19,600,000
Impact of the TCJA Tax Reform, Other Adjustments		400,000
Valuation allowance	3,204,000	$ 1,350,000
Goodwill amortized period		15 years
Unrecognized tax benefits	1,079,000	$ 1,079,000	1,088,000	$ 2,490,000
Unrecognized tax benefit that would impact tax rate	853,000,000,000	853,000
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	9,000	652,000
Income tax-related interest payable	345,000	232,000
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	$ 0	$ 0	$ 848,000
State and Local Jurisdiction | New York State | Minimum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year	2011
State and Local Jurisdiction | New York State | Maximum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year	2014
State and Local Jurisdiction | New York City | Minimum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year	2009
State and Local Jurisdiction | New York City | Maximum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year	2012
Oppenheimer Israel (OPCO) Ltd.
Schedule Of Income Taxes [Line Items]
Net operating loss carryforward	$ 2,500,000
Oppenheimer Europe [Member]
Schedule Of Income Taxes [Line Items]
Valuation allowance	$ 1,800,000