Statements of Operations and Comprehensive Loss (USD $)	3 Months Ended		85 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Income Statement [Abstract]
Revenue
Operating expenses:
Research and development	6,157,928	1,897,795	57,905,773
General and administrative	3,751,319	678,923	19,020,256
Total operating expenses	9,909,247	2,576,718	76,926,029
Operating loss	(9,909,247)	(2,576,718)	(76,926,029)
Other income (expense):
Grant income			1,481,408
Interest income (expense), net	19,025	(754,114)	(4,897,573)
Extinguishment of debt and other liabilities		2,419,766	3,735,499
Reimbursements from Aerpio	193,112	290,152	3,214,203
Gain on cancellation of preferred stock future tranche rights			653,465
Net loss and comprehensive loss	(9,697,110)	(620,914)	(72,739,027)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(9,697,110)	(620,914)	(72,739,027)
Accretion on preferred stock	(86,899,555)	(848,125)	(153,637,754)
Loss on extinguishment of preferred stock			(597,174)
Net loss applicable to common stockholders	$ (96,596,665)	$ (1,469,039)	$ (226,973,955)
Net loss per share applicable to common stockholders-basic and diluted	$ (43.37)	$ (3.09)	$ (669.68)
Weighted-average number of common shares used in net loss per share applicable to common stockholders'-basic and diluted	2,227,058	475,915	338,930