Significant Inputs and Assumptions Used in Binomial Lattice Model for Derivative Liability (Detail) (USD $)	0 Months Ended		6 Months Ended
	Sep. 26, 2014		Nov. 30, 2014		Sep. 26, 2014
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Quoted market price on valuation date	$ 0.79		$ 1.24
Contractual conversion rate			$ 1.00		$ 1.00
Adjusted conversion price	$ 0.9759	[1]	$ 1.0000	[1]
Contractual term to maturity (years)	2 years		1 year 9 months 26 days
Expected volatility	123.00%		120.00%
Contractual interest rate	5.00%		5.00%
Risk-free rate	0.59%		0.29%
Risk adjusted rate	2.69%		3.05%
Probability of event of default	5.00%		5.00%

[1] The adjusted conversion price input used in the Binomial Lattice Model considers the potential for an adjustment to the stated conversion price due to a future dilutive issuance. This input was calculated using a probability-weighted approach which considered the likelihood of various scenarios occurring including (i) potential success or failure of various phases for PRO 140, (ii) the probability the Company will enter into a future financing and (iii) and the potential price of a future financing.