Amortization Expense of Acquired Intangibles (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Amortization expense:
Total amortization expense	$ 3,457	$ 2,772	$ 10,637	$ 8,322
Cost of revenue
Amortization expense:
Total amortization expense	1,382	1,540	4,666	4,622
Selling and marketing
Amortization expense:
Total amortization expense	1,501	1,232	4,496	3,696
General and administrative
Amortization expense:
Total amortization expense	$ 574		$ 1,475	$ 4