Convertible Notes, Convertible Preferred Stock and Common and Preferred Stock Warrants - Warrants Outstanding and Respective Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Series F warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	0	581,182
Warrants and Rights Outstanding	$ 0	$ 8,378
Series G warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	0	279,606
Warrants and Rights Outstanding	$ 0	$ 1,447
Preferred stock warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	0	860,788
Warrants and Rights Outstanding	$ 0	$ 9,825