Stockholders' Equity - Common Stock and Warrants (Details) $ / shares in Units, $ in Thousands						1 Months Ended			12 Months Ended
	Dec. 02, 2019 USD ($)	Oct. 29, 2019 USD ($)	Apr. 12, 2017 USD ($) $ / shares shares	Apr. 03, 2017 USD ($) $ / shares	Dec. 22, 2016 $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) item $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Mar. 31, 2018 USD ($)	Jul. 20, 2017 $ / shares
Stockholders' equity
Preferred stock, Shares authorized | shares						5,000,000			5,000,000
Preferred stock, par value | $ / shares						$ 0.01			$ 0.01
Common Stock Shares, Outstanding | shares						303,378,515			303,378,515	219,157,998
Common stock, par value (in dollars per share) | $ / shares				$ 0.01		$ 0.01			$ 0.01	$ 0.01
Principal amount												$ 100,000
Maturity principal amount							$ 48,000
Proceeds from issuance of debt									$ 39,052	$ 95,856
Number of votes per share | item									1
Common stock shares issued | shares								10,000,000
Par value, common stock | $ / shares				$ 0.01		0.01			$ 0.01	$ 0.01
Share price (in dollars per share) | $ / shares								$ 2.35
Proceeds from public offerings, net of transaction costs								$ 23,500	$ 158,428	$ 7,195	$ 22,992
Exercise price of warrants (in dollars per share) | $ / shares													$ 2.1231
Value of shares issued									$ 158,429	$ 7,016	$ 22,992
Series A Junior Participating Cumulative Preferred Stock
Stockholders' equity
Preferred stock, par value | $ / shares						$ 0.01			$ 0.01	$ 0.01
Common Stock Shares, Outstanding | shares						0			0	0
At Market Issuance Sales Agreement
Stockholders' equity
Common stock shares issued | shares									6,300,000
Proceeds from public offerings, net of transaction costs									$ 14,500
Authorized amount				$ 75,000
Value of shares issued	$ 46,800	$ 46,800
Gross proceeds from sales of fixed combination of the shares and the warrants									$ 15,300
Public Offerings
Stockholders' equity
Common stock shares issued | shares						46,000,000		10,000,000	46,000,000
Share price (in dollars per share) | $ / shares						$ 2.75		$ 2.35	$ 2.75
Proceeds from public offerings, net of transaction costs						$ 120,400			$ 120,400
Warrants issued in December 2016
Stockholders' equity
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares			5,250,750
Class of Warrant or Right Issued | shares					10,501,500
Exercise price of warrants (in dollars per share) | $ / shares					$ 1.50
Number of warrants exercised (in shares) | shares			10,501,500
Proceeds from exercise of warrants, net of transaction costs			$ 15,100
Shares of common stock that can be purchased from warrants issued | shares			5,250,750
Per share price of shares of common stock | $ / shares			$ 2.69
Warrant Issued With Amazon And Walmart Stores Inc Transaction Agreement In 2017
Stockholders' equity
Number of warrants exercised (in shares) | shares									26,188,434	26,188,434
Warrant Issued With Amazon And Walmart Stores Inc Transaction Agreement In 2017 | Maximum
Stockholders' equity
Class of Warrant or Right Issued | shares											110,573,392
$40M Convertible Senior Note
Stockholders' equity
Principal amount						48,000	$ 40,000		$ 48,000
Interest rate (as a percent)							7.50%
Maturity principal amount							$ 48,000
Long-term borrowings						$ 39,600			$ 39,600
Proceeds from issuance of debt							$ 39,100
Share price (in dollars per share) | $ / shares						$ 3.16			$ 3.16