Selected Quarterly Financial Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Data (Unaudited) [Abstract]
Total operating expenses	$ 10,939,000	$ 10,277,000	$ 9,264,000	$ 9,032,000	$ 8,871,000	$ 8,485,000	$ 4,961,000	$ 4,182,000	$ 39,512,146	$ 26,498,818	$ 13,194,183
Loss from operations	(10,939,000)	(10,277,000)	(9,264,000)	(9,032,000)	(8,871,000)	(8,485,000)	(4,961,000)	(4,182,000)	(39,512,146)	(26,498,818)	(13,194,183)
Net loss	(9,516,000)	(10,759,000)	(9,376,000)	(9,170,000)	(7,960,000)	(10,130,000)	(5,521,000)	(4,468,000)	(38,820,998)	(28,078,646)	(12,201,386)
Comprehensive loss	(9,516,000)	(10,759,000)	(9,376,000)	(9,170,000)	(7,960,000)	(10,130,000)	(5,521,000)	(4,468,000)	(38,820,998)	(28,078,646)	(12,201,386)
Net loss attributable to common stockholders	$ (9,516,000)	$ (10,759,000)	$ (9,376,000)	$ (9,170,000)	$ (8,058,000)	$ (11,958,000)	$ (7,267,000)	$ (5,152,000)	$ (38,820,998)	$ (32,435,054)	$ (13,782,087)
Loss per share attributable to common stockholders basic and diluted (in dollars per share)	$ (0.33)	$ (0.37)	$ (0.33)	$ (0.32)	$ (0.30)	$ (7.08)	$ (4.30)	$ (3.05)	$ (1.34)	$ (4.01)	$ (8.16)