Statements of Operations and Comprehensive Income (Loss) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenue:
Collaboration revenue	$ 1,875,000	$ 1,875,000	$ 3,750,000	$ 2,500,000
Total revenue	1,875,000	1,875,000	3,750,000	2,500,000
Operating expenses:
General and administrative	3,696,682	3,107,263	7,614,432	6,196,885
Research and development	17,203,345	10,275,470	32,956,432	20,874,463
Total operating expenses	20,900,027	13,382,733	40,570,864	27,071,348
Loss from operations	(19,025,027)	(11,507,733)	(36,820,864)	(24,571,348)
Other income (expense):
Change in fair value of warrant liability	28,234	5,348	69,721	(3,065)
Gain on asset disposal		2,656		2,656
Miscellaneous income			221,699	173,535
Interest income	214,376	53,219	407,213	92,688
Interest expense	(433,901)	(72,341)	(873,066)	(142,962)
Total other (expense) income	(191,291)	(11,118)	(174,433)	122,852
Net loss	(19,216,318)	(11,518,851)	(36,995,297)	(24,448,496)
Net loss attributable to common stockholders	(19,216,318)	(11,518,851)	(36,995,297)	(24,448,496)
Other comprehensive income, net:
Unrealized gains on marketable securities	44,979	2,127	280,973	28,884
Other comprehensive income	44,979	2,127	280,973	28,884
Comprehensive loss	$ (19,171,339)	$ (11,516,724)	$ (36,714,324)	$ (24,419,612)
Per share information:
Net loss per share of common stock, basic and diluted (in dollars per share)	$ (0.37)	$ (0.28)	$ (0.71)	$ (0.61)
Weighted average common shares outstanding, basic and diluted (in shares)	52,174,569	40,809,931	51,762,467	40,034,864