Issue of options under equity incentive plan - Narrative (Detail) (2010 Equity Incentive Plan [Member], USD $)	1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended
	May 31, 2011 Options Granted May 2011 [Member]	Apr. 30, 2014 Options Granted May 2011 [Member]	Oct. 31, 2013 Options Granted May 2011 [Member]	Dec. 31, 2010 Options Granted December 13, 2010 [Member]	Apr. 30, 2014 Options Granted December 13, 2010 [Member]	Oct. 31, 2013 Options Granted December 13, 2010 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	750,000			2,500,000
Employee stock option vesting rights		The options vested 1/3 upon grant date, 1/3 vested on February 1, 2012 and the balance vested on February 1, 2013.			1/3 on December 13, 2010, 1/3 vested on November 17, 2011 and the balance vested on November 17, 2012.
Stock options expiration date		Feb. 01, 2018			Nov. 17, 2020
Number of options, outstanding		750,000	750,000		2,500,000	2,500,000
Weighted average grant date fair value per option granted		$ 0.95			$ 0.81
Weighted average remaining contractual life		3 years 9 months			6 years 6 months
Options exercisable		750,000			2,500,000