Summary of Significant Accounting Policies - Activity of Allowance for Doubtful Accounts (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 286	$ 378
Charges to costs and expenses	23	(54)
Accounts charged off, less recoveries	(120)	(38)
Ending balance	$ 189	$ 286