Fixed Assets - Schedule of Fixed Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Less accumulated depreciation and amortization	$ (4,318)	$ (3,261)
Total	11,004	11,748
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	1,870	1,739
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	2,435	2,393
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 11,017	$ 10,877