Quarterly Financial Data (unaudited) - Summary of Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	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
Quarterly Financial Data [Abstract]
Revenues	$ 28,550	$ 3,550	$ 3,549	$ 3,550	$ 3,550	$ 3,550	$ 3,549	$ 3,550	$ 39,199	$ 14,199	$ 5,916
Total operating expenses	14,365	12,814	13,335	11,990	11,434	8,972	8,625	8,381	52,504	37,412	23,134
Net profit/(loss) attributable to common stockholders	$ 14,259	$ (9,231)	$ (9,760)	$ (8,420)	$ (8,540)	$ (7,388)	$ (6,782)	$ (5,485)	$ (13,152)	$ (28,195)	$ (19,851)
Net profit/(loss) per common share, basic	$ 0.46	$ (0.35)	$ (0.37)	$ (0.32)
Net profit/(loss) per common share, diluted	$ 0.44	$ (0.35)	$ (0.37)	$ (0.32)
Weighted average number of shares, basic	30,878,973	26,470,298	26,337,184	26,169,152					28,104,991	7,594,115	3,394,727
Weighted average number of shares, diluted	32,228,172	26,470,298	26,337,184	26,169,152
Net loss per common share, basic and diluted					$ (0.48)	$ (2.78)	$ (2.78)	$ (2.47)	$ (0.48)	$ (4.48)	$ (11.30)