Stockholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended		48 Months Ended	80 Months Ended	9 Months Ended		12 Months Ended	48 Months Ended			1 Months Ended	48 Months Ended	0 Months Ended
	Aug. 31, 2013	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Aug. 02, 2013	Dec. 31, 2013 Research and development expense [Member]	Dec. 31, 2012 Research and development expense [Member]	Dec. 31, 2013 General and administrative expense [Member]	Dec. 31, 2012 General and administrative expense [Member]	Dec. 31, 2012 Restricted stock [Member]	Dec. 31, 2013 Restricted stock [Member]	Dec. 31, 2012 Restricted stock [Member]	Dec. 31, 2011 Restricted stock [Member]	Dec. 31, 2013 Restricted stock [Member]	Dec. 31, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2013 Equity Incentive Plan 2008 [Member]	Mar. 31, 2012 Equity Incentive Plan 2008 [Member]	Dec. 31, 2011 Equity Incentive Plan 2008 [Member]	Aug. 31, 2013 Equity Incentive Plan 2012 [Member]	Jan. 31, 2012 Equity Incentive Plan 2012 [Member]	Nov. 30, 2013 Equity Distribution Agreement [Member]	Dec. 31, 2011 Other Plan [Member] Restricted stock [Member]	Aug. 02, 2013 Underwriting Agreement [Member]	Jul. 17, 2013 Underwriting Agreement [Member]	Aug. 02, 2013 Underwriting Agreement [Member] Over Allotment Option Exercised [Member]
Class of Stock [Line Items]
Shares authorized under shelf registration statement		150,000,000	150,000,000		150,000,000																						100,000,000
Issuance of common stock		77,424,956	64,686,919		77,424,956																					10,350,000		1,350,000
Offering price per share								$ 4.50																		$ 4.23
Proceeds from issuance of common stock																										$ 43,400,000
Underwriting discounts and commissions and other offering expenses																										3,200,000
Common stock issued through investment bank	10,350,000																							4,000,000
Number of shares issuable upon exercise of warrant		533,533		11,612,791	2,404,519	13,423,622
Common shares authorized to be issued																			1,521,584			5,000,000	6,553,986
Shares issued during the year																			0	0
Termination date of Equity Incentive Plan																			Jul. 01, 2018
Restricted common stock to founders																1,258,934					1,086,662				172,272
Shares available for issuance																						11,553,986
Termination date of Equity Incentive Plan					10 years
Restricted stock issued													1,380,000		1,380,000
Issuance restricted Common stock to certain employees, advisors and consultants			55,000		60,000		1,380,000											60,000
Restricted stock cancelled		3,703		9,021	164,243	89,674
Restricted stock units vested during the period		8,750		21,250	305,000	211,250
Total employee stock-based compensation recorded as operating expenses									12,000	82,000	669,000	750,000		681,000	834,000		1,837,000
Unrecognized stock-based compensation expense														$ 883,000			$ 883,000
Unrecognized stock-based compensation expense recognition maximum weighted average period														1 year 8 months 12 days