Warrants - Summary of Warrant Activity (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Number of warrants outstanding (shares), beginning balance	5,452,923
Number of warrants granted during the period (shares)	2,732,682
Number of warrants exercised during the period (shares)	(612,923)
Number of warrants expired during the period (share)	(179,716)
Number of warrants outstanding (shares), ending balance	7,392,966
Warrants exercise price (usd per share), beginning balance | $ / shares	$ 11.32
Weighted-average exercise price, warrants granted during the period (usd per share) | $ / shares	2.87
Weighted-average exercise price, warrants exercised during the period (usd per share) | $ / shares	0.85
Weighted-average exercise price, warrants expired during the period (usd per share) | $ / shares	81.18
Warrants exercise price (usd per share), ending balance | $ / shares	$ 7.36
Warrants
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Number of warrants outstanding (shares), beginning balance	1,385,556
Number of warrants granted during the period (shares)	0
Number of warrants exercised during the period (shares)	0
Number of warrants expired during the period (share)	(179,716)
Number of warrants outstanding (shares), ending balance	1,205,840
Warrants
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Number of warrants outstanding (shares), beginning balance	4,067,367
Number of warrants granted during the period (shares)	2,732,682
Number of warrants exercised during the period (shares)	(612,923)
Number of warrants expired during the period (share)	0
Number of warrants outstanding (shares), ending balance	6,187,126