Consolidated Statements of Financial Condition (Parenthetical) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Allowance for receivable from brokers	$ 551,000	$ 1,550,000
Allowance for receivable from customers	2,040,000	1,736,000
Assets
Fixed assets, accumulated depreciation and amortization (in dollars)	33,150,000	28,355,000
Intangible assets, accumulated amortization (in dollars)	$ 37,038,000	$ 33,081,000
Stockholders' equity
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	120,750	120,750
Preferred stock, shares outstanding	120,750	120,750
Preferred Stock, Liquidation Preference, Value	$ 120,750,000	$ 120,750,000
Treasury Stock, Shares	14,092,732	12,133,276
Common Stock Class A
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	62,500,000	62,500,000
Common stock, shares issued	43,235,279	41,765,296
Common stock, shares outstanding	29,142,547	29,632,020
Common stock, restricted shares	253,772	191,962
Treasury Stock, Shares	14,092,732	12,133,276
Common Stock Class B
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	62,500,000	62,500,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0