Other Balance Sheet Accounts - Summary of Accounts Payable and Accrued Expenses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Payables And Accruals [Abstract]
Employee compensation	$ 2,356	$ 3,858
Post-termination benefit accrual	767
Clinical trial accrual	656	660
Accounts payable	574	377
Deferred rent	353	307
Other accrued liabilities	467	427
Total accounts payable and accrued expenses	$ 5,173	$ 5,629