Summary of Siginificant Accounting Policies - Stock-Based Compensation, Per Share Amounts (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended								12 Months Ended
	Dec. 31, 2016	Jan. 31, 2014	Feb. 28, 2013	May 31, 2011	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 22, 2016	May 16, 2013	Dec. 31, 2011
Stock-Based Compensation
Tax benefit (expense) for stock-based compensation													$ 0	$ 0	$ 0
Numerator
Net loss attributable to common shareholders					$ (19,237)	$ (13,420)	$ (13,154)	$ (11,780)	$ (25,227)	$ (10,238)	$ (9,253)	$ (11,077)	$ (57,591)	$ (55,795)	$ (88,644)
Denominator
Weighted Average Number of Shares Outstanding, Basic and Diluted													180,619,860	176,067,231	159,228,815
Number of dilutive potential common shares													46,765,065	21,652,391	18,614,650
Granted (in shares)													3,702,500	3,960,000	4,245,000
Number of warrants exercised (in shares)													119,879	26,882	23,918,429
Weighted average exercise price of warrants (in dollars per share)	$ 1.50				$ 1.50								$ 1.50
Warrants outstanding (in shares)	14,501,600				14,501,600				4,192,567				14,501,600	4,192,567
Stock options
Denominator
Number of dilutive potential common shares													14,760,054	11,700,786	8,367,271
Restricted stock
Denominator
Number of dilutive potential common shares													13,333	204,444	473,336
Warrants
Denominator
Number of dilutive potential common shares													14,501,600	4,192,567	4,219,449
Preferred stock
Denominator
Number of dilutive potential common shares													17,490,078	5,554,594	5,554,594
Warrants issued in May, 2011
Denominator
Number of warrants issued (in shares)				7,128,563
Weighted average exercise price of warrants (in dollars per share)				$ 0.93
Warrants outstanding (in shares)	0				0				192,467				0	192,467	219,349				22,995,365
Warrants issued in February, 2013
Denominator
Number of warrants issued (in shares)			23,637,500
Weighted average exercise price of warrants (in dollars per share)			$ 0.15
Warrants outstanding (in shares)	100				100				100				100	100	100
Warrants issued in February, 2013 | Minimum
Denominator
Weighted average exercise price of warrants (in dollars per share)																$ 0.15
Warrants issued in January, 2014
Denominator
Number of warrants issued (in shares)		4,000,000
Number of warrants exercised (in shares)													0	0	0
Weighted average exercise price of warrants (in dollars per share)	$ 1.025	$ 4.00			$ 1.025								$ 1.025		$ 4.00
Warrants issued in December 2016
Denominator
Number of warrants issued (in shares)	10,501,500
Number of warrants exercised (in shares)													0
Weighted average exercise price of warrants (in dollars per share)	$ 1.50				$ 1.50								$ 1.50
Series C Redeemable Convertible Preferred Stock
Denominator
Redeemable convertible Preferred Stock, shares issued	5,231				5,231				5,231				5,231	5,231				10,431
Shares issued upon conversion of redeemable stock (in shares)																5,200
Series D Redeemable Convertible Preferred Stock
Denominator
Redeemable convertible Preferred Stock, shares issued	18,500				18,500				0				18,500	0			18,500
Shares issued upon conversion of redeemable stock (in shares)													0