Condensed Statements of Operations and Comprehensive Loss (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement [Abstract]
Revenue
Operating expenses:
Research and development	5,524,895	2,453,000	11,682,823	4,350,796
General and administrative	2,315,101	667,783	6,066,420	1,346,706
Total operating expenses	7,839,996	3,120,783	17,749,243	5,697,502
Operating loss	(7,839,996)	(3,120,783)	(17,749,243)	(5,697,502)
Other income (expense):
Interest income (expense), net	50,442	2,906	69,466	(751,207)
Extinguishment of debt and other liabilities				2,419,766
Reimbursements from Aerpio	171,227	287,445	364,339	577,597
Net loss	(7,618,327)	(2,830,432)	(17,315,438)	(3,451,346)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(7,618,327)	(2,830,432)	(17,315,438)	(3,451,346)
Accretion on preferred stock		(49,265,010)	(86,899,555)	(50,113,135)
Net loss applicable to common stockholders	(7,618,327)	(52,095,442)	(104,214,993)	(53,564,481)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.39)	$ (103.19)	$ (9.48)	$ (109.21)
Weighted-average number of common shares used in net loss per share applicable to common stockholders' - basic and diluted	19,652,056	504,868	10,987,692	490,472
Comprehensive loss
Net loss	(7,618,327)	(2,830,432)	(17,315,438)	(3,451,346)
Other comprehensive loss, net of deferred tax:
Unrealized loss on securities, net of tax of $0	(8,216)		(8,216)
Comprehensive loss	$ (7,626,543)	$ (2,830,432)	$ (17,323,654)	$ (3,451,346)