Stockholders' Equity - Additional Information 1 (Detail) (USD $)	3 Months Ended		6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		77 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				1 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Research and development expense [Member]	Sep. 30, 2012 Research and development expense [Member]	Sep. 30, 2013 Research and development expense [Member]	Sep. 30, 2012 Research and development expense [Member]	Sep. 30, 2013 General and administrative expense [Member]	Sep. 30, 2012 General and administrative expense [Member]	Sep. 30, 2013 General and administrative expense [Member]	Sep. 30, 2012 General and administrative expense [Member]	Sep. 30, 2013 Stock options [Member]	Sep. 30, 2012 Stock options [Member]	Sep. 30, 2013 Stock options [Member]	Sep. 30, 2012 Stock options [Member]	Sep. 30, 2013 Stock options [Member]	Sep. 30, 2013 Stock options [Member] Research and development expense [Member]	Sep. 30, 2012 Stock options [Member] Research and development expense [Member]	Sep. 30, 2013 Stock options [Member] Research and development expense [Member]	Sep. 30, 2012 Stock options [Member] Research and development expense [Member]	Sep. 30, 2013 Stock options [Member] General and administrative expense [Member]	Sep. 30, 2012 Stock options [Member] General and administrative expense [Member]	Sep. 30, 2013 Stock options [Member] General and administrative expense [Member]	Sep. 30, 2012 Stock options [Member] General and administrative expense [Member]	Sep. 30, 2013 2008 Plan [Member]	Oct. 12, 2011 2008 Plan [Member]	Oct. 12, 2011 2008 Plan [Member] Stock options [Member]	Sep. 30, 2013 2008 Plan [Member] Stock options [Member]	Sep. 30, 2013 2012 Plan [Member]	Sep. 30, 2012 2012 Plan [Member]	Sep. 30, 2013 2012 Plan [Member]	Sep. 30, 2012 2012 Plan [Member]	Sep. 30, 2013 2012 Plan [Member] Stock options [Member]
Class of Stock [Line Items]
Equity Incentive Plan, shares	160,540	927,981	574,540	2,023,394																								896,256
Granted incentive stock options to purchase shares of Common stock, exercise price																											$ 0.08
Restricted stock vesting conditions																													A quarter of which vested on the one year anniversary of employment, in May 2012, and the remaining options are vesting ratably over the remaining 36 month term					A quarter of which will vest on either the one year anniversary of employment or the one year anniversary of the vesting commencement date
Remaining options vest																										36 months						36 months
Issuances of Common stock from stock option exercises, Shares			7,300	224,064																										229,540	1,296,903	281,040	1,602,561
Stock option granted, Restricted portion																														246,000	126,000	291,500	126,000
Stock option granted, Quarterly vesting restricted term																																3 years
Weighted average remaining contractual term of options exercisable			8 years 8 months 12 days
Weighted average remaining contractual term of options outstanding			8 years 10 months 24 days
Total employee stock-based compensation recorded as operating expenses					$ 4,000	$ 84,000	$ 8,000	$ 84,000	$ 127,000	$ 914,000	$ 525,000	$ 914,000	$ 1,155,000	$ 244,000	$ 1,555,000	$ 283,000	$ 2,534,000	$ 66,000	$ 16,000	$ 133,000	$ 51,000	$ 1,089,000	$ 228,000	$ 1,422,000	$ 232,000
Total unrecognized compensation cost related to unvested stock option grants	$ 5,406,000		$ 5,406,000
Total unrecognized compensation cost related to unvested stock option grants, weighted average period															3 years 9 months 18 days