Stockholders' Equity - Common Stock and Warrants (Details)				1 Months Ended		3 Months Ended		12 Months Ended		24 Months Ended
	Apr. 12, 2017 USD ($) $ / shares shares	Apr. 03, 2017 USD ($) $ / shares	Dec. 22, 2016 $ / shares shares	Mar. 31, 2019 USD ($) $ / shares shares	Feb. 28, 2018 shares	Mar. 31, 2019 USD ($) item $ / shares shares	Mar. 31, 2018 USD ($)	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares	Mar. 31, 2019 USD ($) $ / shares shares	Jul. 20, 2017 $ / shares	Dec. 31, 2016 $ / shares shares
Stockholders' equity
Preferred stock, Shares authorized | shares				5,000,000		5,000,000				5,000,000
Preferred stock, par value | $ / shares				$ 0.01		$ 0.01				$ 0.01
Common Stock Shares, Outstanding | shares				229,534,572		229,534,572		219,157,998		229,534,572
Common Stock, par value (in dollars per share) | $ / shares				$ 0.01		$ 0.01		$ 0.01		$ 0.01
Number of votes per share | item						1
Common stock shares issued | shares				10,000,000		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		$ 2.35				2.35
Proceeds from public offerings, net of transaction costs | $				$ 23,500,000		$ 23,498,000
Exercise price of warrants (in dollars per share) | $ / shares											$ 2.1231
Proceeds from exercise of warrants, net of transaction costs | $							$ 50,000
Value of shares issued | $						$ 23,498,000
Series A Junior Participating Cumulative Preferred Stock
Stockholders' equity
Preferred stock, par value | $ / shares				$ 0.01		$ 0.01		$ 0.01		$ 0.01
Common Stock Shares, Outstanding | shares				0		0		0		0
At Market Issuance Sales Agreement
Stockholders' equity
Common Stock, par value (in dollars per share) | $ / shares		$ 0.01
Par value, common stock | $ / shares		$ 0.01
Authorized amount | $		$ 75,000,000
Value of shares issued | $										$ 30,200,000
Warrants issued in February, 2013
Stockholders' equity
Exercise price of warrants (in dollars per share) | $ / shares									$ 0.15			$ 0.15
Warrants outstanding (in shares) | shares									100			100
Number of warrants exercised (in shares) | shares					100
Warrants issued in December 2016
Stockholders' equity
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 | $	$ 15.10
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						18,913,869		18,913,869
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