Amortization Expense of Acquired Intangibles (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 3,105	$ 3,599	$ 9,479	$ 10,168
Cost of revenue
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	1,232	1,642	3,871	4,626
Selling and marketing
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 1,873	1,867	$ 5,608	5,274
General and administrative
Acquired Finite-Lived Intangible Assets [Line Items]
Total amortization expense		$ 90		$ 268