Warrants - Warrant Activity (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	27,264,165
Number of warrants granted during the period (shares)	0
Number of warrants exercised during the period (shares)	(2,416,104)
Number of warrants expired during the period (shares)	0
Ending balance, number of warrants outstanding (shares)	24,848,061
Beginning balance, weighted-average exercise price (usd per share) | $ / shares	$ 2.26
Weighted-average exercise price, warrants granted during the period (usd per share) | $ / shares	0.00
Weighted-average exercise price, warrants exercised during the period (usd per share) | $ / shares	0.01
Weighted-average exercise price, warrants expired during the period (usd per share) | $ / shares	0.00
Ending balance, weighted-average exercise price (usd per share) | $ / shares	$ 2.48
Warrant
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	6,927,413
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)	0
Ending balance, number of warrants outstanding (shares)	6,927,413
Warrant
Increase (Decrease) in Warrants Outstanding [Roll Forward]
Beginning balance, number of warrants outstanding (shares)	20,336,752
Number of warrants granted during the period (shares)	0
Number of warrants exercised during the period (shares)	(2,416,104)
Number of warrants expired during the period (shares)	0
Ending balance, number of warrants outstanding (shares)	17,920,648