Warrants - Warrant Activity (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	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 (shares)	(75,040)
Ending balance, number of warrants outstanding (shares)	7,497,642
Beginning balance, weighted-average exercise price (usd per share) | $ / 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	37.50
Ending balance, weighted-average exercise price (usd per share) | $ / shares	$ 8.83
Warrant
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	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 (shares)	(75,040)
Ending balance, number of warrants outstanding (shares)	1,310,516
Warrant
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	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 (shares)	0
Ending balance, number of warrants outstanding (shares)	6,187,126