Quarterly report pursuant to Section 13 or 15(d)

Property and Equipment - Schedule Of Interest Expenses For Debt Arrangements (Detail)

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Property and Equipment - Schedule Of Interest Expenses For Debt Arrangements (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2017
Sep. 30, 2017
Dec. 31, 2016
Property, Plant and Equipment [Line Items]      
Property and equipment, net   $ 8,221 $ 7,376
National Holdings [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 2,506    
Less: accumulated depreciation (314)    
Property and equipment, net 2,192    
Equipment [Member] | National Holdings [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment 1,305    
Furniture And Fixtures [Member] | National Holdings [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 240    
Property, Plant and Equipment, Estimated Useful Lives 5 years    
Leaseholds And Leasehold Improvements [Member] | National Holdings [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 685    
Property, Plant and Equipment, Estimated Useful Lives Lesser of useful life or term of lease    
Capital leases (primarily composed of computer equipment) [Member] | National Holdings [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 276    
Property, Plant and Equipment, Estimated Useful Lives 5 years    
National Holdings Corporation [Member] | Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Estimated Useful Lives 5 years