Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 5,100	$ 6,500	$ 4,800
Charge related to disposal of property and equipment		493	$ 4
Gain on sale of property and equipment	$ 439	40
Maximum [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of property and equipment		$ 100