Stockholders' Equity - Common Stock Warrants (Details) - Warrants for the purchase of common stock	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Common Stock Warrants
Warrants Outstanding (in shares) | shares	9,183,885
Weighted Average
Common Stock Warrants
Exercise Price (in dollars per share) | $ / shares	$ 6.99
Weighted average life (in years)	4 years 6 months 18 days
Warrants Issued in 2014
Common Stock Warrants
Warrants Outstanding (in shares) | shares	1,227
Exercise Price (in dollars per share) | $ / shares	$ 122.12
Warrants Issued in 2015
Common Stock Warrants
Warrants Outstanding (in shares) | shares	1,227
Exercise Price (in dollars per share) | $ / shares	$ 122.12
Warrants Issued in 2018
Common Stock Warrants
Warrants Outstanding (in shares) | shares	4,199,995
Exercise Price (in dollars per share) | $ / shares	$ 12.00
Warrants Issued in 2019
Common Stock Warrants
Warrants Outstanding (in shares) | shares	1,991,300
Exercise Price (in dollars per share) | $ / shares	$ 6.25
Warrants Issued In 2021
Common Stock Warrants
Warrants Outstanding (in shares) | shares	2,990,136
Exercise Price (in dollars per share) | $ / shares	$ 0.35