Future Payments (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Remainder of 2013	$ 575
2014	3,995
2015	3,699
2016	3,403
Total minimum payments	11,672
Less amount representing interest	(1,672)
Notes payable, gross	10,000
Discount on notes payable	(135)
Accretion of the final exit fee payment	67
Notes Payable	9,932
Less short-term portion of notes payable	(2,383)
Long-term notes payable	$ 7,549	$ 9,826