Amortization Expense Included in Condensed Consolidated Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Amortization expense	$ 293	$ 424	$ 1,163	$ 2,844	$ 3,277
Cost of revenue
Amortization expense	96	91	289	794
Selling and marketing
Amortization expense	$ 197	$ 333	$ 874	$ 2,050