Notes Payable - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended				1 Months Ended		1 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Oct. 21, 2010	Oct. 31, 2010 Tranche 1	Oct. 21, 2010 Tranche 1	Mar. 31, 2011 Tranche 2	Mar. 25, 2011 Tranche 2
Debt Instrument [Line Items]
Loan and security agreement amount						$ 20,000,000		$ 10,000,000		$ 10,000,000
Number of tranches						2
Loan and security agreement, annual fixed rate of interest								8.55%		8.56%
Final payment fee, percentage of amount borrowed								5.00%		4.00%
Final payment fee, amount								500,000		400,000
Debt issuance costs							169,000		58,000
Total non-cash interest expense associated with borrowings, amortization of the discount	78,000	76,000	161,000	118,000
Total non-cash interest expense associated with borrowings, amortization of debt issuance costs	19,000	19,000	39,000	33,000
Unamortized balance of debt discount	428,000		428,000		589,000
Unamortized balance of debt issuance costs	$ 106,000		$ 106,000		$ 145,000