Furniture, Equipment and Leasehold Improvements, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Furniture and office equipment	$ 7,564	$ 5,933
Computer equipment and software	9,274	7,330
Leasehold improvements	14,132	11,334
Furniture, equipment and leasehold improvements, gross	30,970	24,597
Accumulated depreciation and amortization	(20,137)	(16,869)
Furniture, equipment and leasehold improvements, net	$ 10,833	$ 7,728