Property and Equipment, Net of Accumulated Depreciation (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,700	$ 3,000
Less accumulated depreciation	(1,600)	(1,400)
Property and equipment, net	$ 2,125	$ 1,603