Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Mar. 15, 2019	Mar. 15, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Convertible preferred stock issued (in shares)				3,171,000,000		5,750,000
Proceeds from issuance of preferred stock, net of offering costs				$ 27,044	$ 0	$ 0
Stock issuance costs			$ 800	335
Decrease in convertible preferred stock				$ 1,100
Series A Preferred Stock
Class of Stock [Line Items]
Convertible preferred stock issued (in shares)			27,850
Conversion price of common stock (usd per share)			$ 2.00
Preferred stock, aggregate voting power equivalent for director election			5.00%
Preferred stock, minimum shares outstanding to trigger certain amendment protections (in shares)			1,392
Preferred stock, approval percentage required to override protective provisions		66.67%
Preferred stock, minimum shares outstanding to trigger certain share issuance protections (in shares)			11,140
Ownership percentage standstill trigger				5.00%
Preferred Stock
Class of Stock [Line Items]
Conversion of stock, shares converted (in shares)				1,100
Common Stock
Class of Stock [Line Items]
Conversion of stock, shares converted (in shares)				550,000
Threshold exercise price for conversion (in dollars per share)				$ 6
Scenario, Forecast | Common Stock
Class of Stock [Line Items]
Threshold exercise price for conversion (in dollars per share)	$ 8