Earnings Per Share - Dilutive Potential Common Shares (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended		3 Months Ended		12 Months Ended
	Nov. 01, 2018	Apr. 12, 2017	Dec. 22, 2016	May 16, 2013	Jan. 31, 2020	Apr. 30, 2017	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018	Mar. 08, 2018	Jul. 31, 2017	Jul. 20, 2017	Apr. 04, 2017
Earnings Per Share
Number of dilutive potential common stock									200,327,965	201,692,250	138,713,090
Exercise price of warrants (in dollars per share)															$ 2.1231
Number of preferred shares that had been converted to common stock							30,962
Principal amount												$ 100,000
Stock options
Earnings Per Share
Stock options granted									3,221,892	2,679,667	5,485,863
Warrants issued in December 2016
Earnings Per Share
Number of warrants issued (in shares)			10,501,500
Shares of common stock that can be purchased from warrants issued (in shares)		5,250,750
Number of warrants exercised (in shares)		10,501,500
Exercise price of warrants (in dollars per share)			$ 1.50
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
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										55,286,696
Warrant shares vested (in shares)							20,368,782		20,368,782	20,368,782
Number of warrants exercised (in shares)									0
Tranche one of warrants issued with the Amazon.com, Inc transaction agreement
Earnings Per Share
Warrant shares vested (in shares)																5,819,652
Warrants issued with the Walmart transaction agreement
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)														55,286,696
Tranche one of warrants issued with the Walmart Stores Inc transaction agreement
Earnings Per Share
Warrant shares vested (in shares)															5,819,652
Series C Preferred Stock
Earnings Per Share
Stock options granted				10,431
Conversion of preferred stock (in shares)											7,811
Series D Redeemable Convertible Preferred Stock
Earnings Per Share
Number of preferred shares that had been converted to common stock											14,800
Shares issued (in shares)			18,500
Number of shares redeemed											3,700
Series E Preferred Stock
Earnings Per Share
Number of preferred shares that had been converted to common stock					500
Conversion of preferred stock (in shares)	35,000								30,462
Number of redeemed shares					4,038			4,038
Convertible Senior Notes
Earnings Per Share
Principal amount								$ 40,000				$ 100,000
Interest rate (as a percent)								7.50%				5.50%
$40M Convertible Senior Note
Earnings Per Share
Principal amount							$ 48,000	$ 40,000	$ 48,000
Interest rate (as a percent)								7.50%
$100M Convertible Senior Notes
Earnings Per Share
Principal amount							$ 100,000		$ 100,000			$ 100,000	$ 100,000
Interest rate (as a percent)												5.50%
Stock options
Earnings Per Share
Number of dilutive potential common stock									23,013,590	21,957,150	19,872,029
Restricted stock
Earnings Per Share
Number of dilutive potential common stock									4,608,560	2,347,347	234,744
Stock options granted									3,201,892	2,367,347	234,744
Warrants
Earnings Per Share
Number of dilutive potential common stock									110,573,392	115,824,142	115,824,242
Preferred stock
Earnings Per Share
Number of dilutive potential common stock									2,998,527	17,933,591	2,782,075
Convertible Senior Notes
Earnings Per Share
Number of dilutive potential common stock									59,133,896	43,630,020