Fixed Assets, net - Schedule of Fixed Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Less accumulated depreciation and amortization	$ (5,276)	$ (4,672)
Total	10,028	10,693
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	2,031	1,879
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	2,391	2,449
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 10,882	$ 11,037