Fair Value Hierarchy of Financial Assets Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents (money market accounts)	$ 53,391	$ 13,918
Fair Value Assets And Liabilities Measured On Recurring Basis Net, Total	53,391	13,918
Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique (Approach)	Market	Market
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents (money market accounts)	53,391	13,918
Fair Value Assets And Liabilities Measured On Recurring Basis Net, Total	$ 53,391	$ 13,918