Amortization Expense of Acquired Intangibles (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Amortization expense:
Total amortization expense	$ 3,756	$ 2,777
Cost of revenue
Amortization expense:
Total amortization expense	1,840	1,541
Selling and marketing
Amortization expense:
Total amortization expense	1,496	1,232
General and administrative
Amortization expense:
Total amortization expense	$ 420	$ 4