Amortization Expense Included in Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 447	$ 364
Cost of revenue
Finite Lived Intangible Assets [Line Items]
Amortization expense	149	112
Selling and Marketing Expense
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 298	$ 252