Capital Structure - Warrants (Details) - $ / shares	Dec. 31, 2018	Oct. 31, 2015	Dec. 31, 2014
Common Stock
Common Stock Warrants
Number of shares available under warrant (in shares)	4,024,708
Preferred Stock \| Series B convertible preferred stock
Common Stock Warrants
Number of shares available under warrant (in shares)			625,208
Common stock
Common Stock Warrants
Number of shares available under warrant (in shares)		22,328
Common stock warrants, expiration date of October 2020 \| Common Stock
Common Stock Warrants
Number of shares available under warrant (in shares)	22,328
Exercise price per share (in dollars per share)	$ 8.40
Common stock warrants, expiration date of May 2022 \| Common Stock
Common Stock Warrants
Number of shares available under warrant (in shares)	2,380
Exercise price per share (in dollars per share)	$ 8.68
Common stock warrants expiration date of June 2022 \| Common Stock
Common Stock Warrants
Number of shares available under warrant (in shares)	4,000,000
Exercise price per share (in dollars per share)	$ 12.50