Amortization of Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 2,835	$ 3,105	$ 8,508	$ 9,479
Cost of revenue
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	1,232	1,232	3,695	3,871
Selling and marketing
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 1,603	$ 1,873	$ 4,813	$ 5,608