Income taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Profit (loss) before income taxes for foreign operations	$ 732,000	$ 4,300,000	$ (1,300,000)
Tax credit, investment, amount	20,500,000
Unrecognized deferred tax liability related to earnings of foreign subsidiaries	$ 2,500,000
Goodwill amortized period	15 years
Unrecognized tax benefits	$ 2,490,000	1,583,000	1,574,000	$ 5,236,000
Unrecognized tax benefits that would impact effective tax rate	1,800,000	1,300,000
Reclass to other tax accounts	0	0	$ 4,907,000
Income tax-related interest (benefit) expense	23,000	22,000
Income tax-related interest payable	$ 106,000	$ 83,000
State and Local Jurisdiction | New York State | Minimum
Income Tax Examination [Line Items]
Income tax examination year	2008
State and Local Jurisdiction | New York State | Maximum
Income Tax Examination [Line Items]
Income tax examination year	2011
State and Local Jurisdiction | New York City | Minimum
Income Tax Examination [Line Items]
Income tax examination year	2009
State and Local Jurisdiction | New York City | Maximum
Income Tax Examination [Line Items]
Income tax examination year	2012
Oppenheimer Israel (OPCO) Ltd.
Income Tax Examination [Line Items]
Net operating loss carryforward	$ 1,300,000
Oppenheimer Investments Asia Ltd.
Income Tax Examination [Line Items]
Net operating loss carryforward	1,000,000
Oppenheimer Europe Ltd
Income Tax Examination [Line Items]
Net operating loss carryforward	$ 397,000