Weighted Average Assumptions used to Estimate Fair Value of Stock Option Grants (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2011	Jun. 30, 2012	Sep. 30, 2011
Non-Statutory Stock Options
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected term (years)	7 years 6 months	7 years 1 month 6 days	6 years 8 months 12 days
Expected volatility	95.71%	104.25%	97.35%
Risk-free interest rate	1.47%	1.13%	2.52%
Expected dividends	$ 0	$ 0	$ 0
Incentive Stock Options
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected term (years)			6 years 6 months
Expected volatility			98.54%
Risk-free interest rate			2.46%
Expected dividends			$ 0