Stockholders' Equity - Shares of Common Stock Issuable on Conversion or Exercise of Rights Granted (Details)	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common shares	15,915,473
Unvested (unexercisable) (shares)	2,241,699
Exercise of Issued Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common shares	445,000
2018 Convertible Notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common shares	3,854,959
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common shares	11,615,514