Earnings Per Share - Anti-dilutive Shares (Details) - $ / shares					1 Months Ended						3 Months Ended			9 Months Ended		12 Months Ended
	Apr. 12, 2017	Apr. 05, 2017	Dec. 22, 2016	May 16, 2013	Feb. 28, 2018	Jul. 31, 2017	Apr. 30, 2017	Dec. 31, 2016	Jan. 31, 2014	Feb. 28, 2013	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jul. 20, 2017	Apr. 04, 2017
Earnings Per Share
Number of dilutive potential common shares														186,714,827	138,819,993
Exercise price of warrants (in dollars per share)																	$ 2.1231
Convertible Senior Notes
Earnings Per Share
Conversion price, per share											$ 2.29			$ 2.29
Stock options
Earnings Per Share
Stock options granted											2,170,000	5,030,000		2,654,667	5,480,863
Restricted stock
Earnings Per Share
Stock options granted											2,160,000	0		2,367,347	234,744
Warrants issued in February, 2013
Earnings Per Share
Number of warrants issued (in shares)										23,637,500
Exercise price of warrants (in dollars per share)					$ 0.15					$ 0.15
Number of warrants exercised (in shares)					100
Number of warrants unexercised (in shares)														0	100
Warrants issued in January, 2014
Earnings Per Share
Number of warrants issued (in shares)							4,000,000		4,000,000
Exercise price of warrants (in dollars per share)							$ 0.65	$ 0.65	$ 4.00
Number of warrants exercised (in shares)														4,000,000
Warrants issued in December 2016
Earnings Per Share
Number of warrants issued (in shares)			10,501,500					10,501,500
Exercise price of warrants (in dollars per share)			$ 1.50					$ 1.50
Number of warrants exercised (in shares)	10,501,500															10,501,500
Shares of common stock that can be purchased from warrants issued (in shares)	5,250,750
Warrants issued in April 2017
Earnings Per Share
Number of warrants issued (in shares)							5,250,750
Exercise price of warrants (in dollars per share)							$ 2.69
Number of warrants exercised (in shares)														0
Number of warrants unexercised (in shares)														0
Warrants issued in July 2017
Earnings Per Share
Number of warrants exercised (in shares)						0
Warrants issued with the Amazon.com, Inc transaction agreement
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)																		55,286,696
Warrants issued with the Walmart Stores, Inc transaction agreement
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)																	55,286,696
Series C redeemable convertible preferred stock.
Earnings Per Share
Stock options granted				10,431
Shares issued upon conversion of redeemable stock (in shares)														7,811	5,200
Series D Redeemable Convertible Preferred Stock
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)								7,381,500
Shares issued upon conversion of redeemable stock (in shares)		9,548,393
Shares issued (in shares)			18,500					18,500
Number of shares redeemed													3,700
Number of preferred shares that had been converted to common stock															14,800.00
Stock options
Earnings Per Share
Number of dilutive potential common shares														22,111,243	19,965,599
Restricted stock
Earnings Per Share
Number of dilutive potential common shares														2,367,347	248,077
Warrants
Earnings Per Share
Number of dilutive potential common shares														115,824,142	115,824,242
Preferred stock
Earnings Per Share
Number of dilutive potential common shares														2,782,075	2,782,075
Convertible Senior Notes
Earnings Per Share
Number of dilutive potential common shares														43,630,020
Maximum | Warrants issued in April 2017
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)							55,286,696
Maximum | Warrants issued in July 2017
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)						55,286,696