Condensed Statements of Operations and Comprehensive Loss (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Operating expenses:
Research and development	$ 6,648,000	$ 3,240,000	$ 18,330,000	$ 7,591,000
General and administrative	2,936,000	794,000	9,003,000	2,141,000
Total operating expenses	9,584,000	4,034,000	27,333,000	9,732,000
Operating loss	(9,584,000)	(4,034,000)	(27,333,000)	(9,732,000)
Other income (expense):
Interest income (expense), net	56,000	28,000	125,000	(723,000)
Extinguishment of debt and other liabilities				2,420,000
Reimbursements from Aerpio	180,000	238,000	544,000	816,000
Net loss	(9,348,391)	(3,767,890)	(26,663,829)	(7,219,236)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(9,348,391)	(3,767,890)	(26,663,829)	(7,219,236)
Accretion on preferred stock		(2,748,232)	(86,899,555)	(52,861,367)
Net loss applicable to common stockholders	(9,348,391)	(6,516,122)	(113,563,384)	(60,080,603)
Net loss per share applicable to common stockholders—basic and diluted	$ (0.47)	$ (11.92)	$ (8.16)	$ (117.94)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted	19,691,167	546,714	13,920,651	509,425
Comprehensive loss:
Net loss	(9,348,391)	(3,767,890)	(26,663,829)	(7,219,236)
Other comprehensive loss:
Unrealized loss on securities	(43,000)		(52,000)
Comprehensive loss	$ (9,391,000)	$ (3,768,000)	$ (26,716,000)	$ (7,219,000)