Stockholders' Equity - Private Placement and Preferred Stock (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares
Class of Stock [Line Items]
Number of shares per unit (in shares)	1
Warrant exercise period	5 years
Par value of preferred stock (in dollars per share) | $ / shares	$ 0.001	$ 0.001	$ 0.001
Shares of common stock issued (in shares)		45,017,062	43,058,827
Shares of preferred stock issued (in shares)		4,963	4,963
Shares of preferred stock outstanding (in shares)		4,963	4,963
Preferred Stock
Class of Stock [Line Items]
Percentage of beneficial ownership	9.99%
Securities Purchase Agreement
Class of Stock [Line Items]
Number of capital units sold in private placement transaction (in units)	8,188,804
Gross proceeds from private placement units sold | $	$ 16.5
Net proceeds from private placement units sold | $	$ 15.3
Issue price per share of preferred stock (in dollars per share) | $ / shares	$ 2.015
2016 PIPE
Class of Stock [Line Items]
Shares of common stock issued (in shares)	3,225,804
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Price per unit issued (in dollars per share) | $ / shares	$ 2.015
Number of shares per unit (in shares)	1
Shares issued upon conversion of convertible preferred stock (in shares)	1,000
Series A Convertible Preferred Stock | Private Placement | 2016 PIPE
Class of Stock [Line Items]
Shares of preferred stock issued (in shares)	4,963
Tranche A Warrants
Class of Stock [Line Items]
Number of warrants	1
Number of shares to be purchased by a warrant (in shares)	0.4
Exercise price (in dollars per share) | $ / shares	$ 2.00
Tranche B Warrants
Class of Stock [Line Items]
Number of warrants	1
Number of shares to be purchased by a warrant (in shares)	0.2
Exercise price (in dollars per share) | $ / shares	$ 3.00