Net loss per share - Schedule of Computation of Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended			12 Months Ended							123 Months Ended
	Mar. 12, 2014	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Mar. 31, 2014
Numerator
Net loss and comprehensive loss incurred in the development stage		$ (4,227,678)	$ (1,010,267)								$ (51,502,587)
Accretion for liquidation preference on preferred stock	(1,132,893)	(1,132,893)	(1,157,865)	(5,351,459)	(3,860,140)	(3,303,200)	(2,167,601)	(1,301,400)	(1,008,153)	(441,162)	(18,566,008)
Accretion for share issuance costs on preferred stock	(19,550)	(19,550)	(44,307)	(123,074)	(168,702)	(163,483)	(175,467)	(159,611)	(139,758)	(65,024)	(1,014,667)
Tax expense on preferred stock	(100,291)	(100,291)	(346,091)	(737,925)	(394,908)	(345,587)	(244,251)	(74,743)			(1,897,702)
Reversal of tax payable on preferred stock due to conversion of preferred stock		1,897,702									1,897,702
Extinguishment of remaining share issuance costs due to conversion of preferred stock	(1,458,478)	(439,227)									(439,227)
Total loss attributable to common stockholders		$ (4,021,937)	$ (2,558,530)								$ (71,522,489)
Denominator
Weighted average shares used to compute basic net loss per common share		3,148,481	301,745								398,573
Effect of potentially dilutive securities:
Stock options
Common stock warrants
Weighted average shares used to compute diluted net loss per common share		3,148,481	301,745								398,573
Net loss per share attributable to common stockholders-basic		$ (1.28)	$ (8.48)								$ (179.45)
Net loss per share attributable to common stockholders-diluted		$ (1.28)	$ (8.48)								$ (179.45)