Fair Value of Financial Assets and Liabilities - Derivative Instruments (Tables)

3 Months Ended

Mar. 31, 2015

Derivatives And Fair Value [Line Items]

Schedule of Derivative Liabilities at Fair Value [Table Text Block]

The following fair value hierarchy table presents information about each major category of the Company's financial liabilities measured at fair value on a recurring basis:

	Quoted Prices in Active Markets for Identical Items (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
March 31, 2015
Liabilities
Preferred B stock conversion liability	$	—	$	—	$	19,425,000	$	19,425,000
Warrant liability		—		—		14,727,000		14,727,000
Total liabilities	$	—	$	—	$	34,152,000	$	34,152,000
December 31, 2014
Liabilities
Preferred B stock conversion liability	$	—	$	—	$	12,320,000	$	12,320,000
Warrant liability		—		—		5,826,000		5,826,000
Total liabilities	$	—	$	—	$	18,146,000	$	18,146,000

Fair Value, Liabilities Measured on Recurring Basis [Table Text Block]

The following table sets forth a summary of changes in the fair value of the Company's Series B redeemable convertible preferred stock derivative and warrant liability, which represents a recurring measurement that is classified within Level 3 of the fair value hierarchy, wherein fair value is estimated using significant unobservable inputs:

	Warrant Liability		Preferred B Stock Conversion Liability
Balance as of December 31, 2014	$	5,826,000	$	12,320,000
Issuance of warrants		4,211,000		—
Changes in estimated fair value		4,690,000		7,105,000
Balance as of March 31, 2015	$	14,727,000	$	19,425,000

Redeemable Convertible Preferred Stock [Member]

Derivatives And Fair Value [Line Items]

Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block]

The following assumptions were used at March 31, 2015 and December 31, 2014:

	March 31, 2015															December 31, 2014
				June			July			December			March						June			July			December
	2011			2013			2013			2013			2015			2011			2013			2013			2013
Volatility		105	%		141	%		141	%		152	%		141	%		155	%		155	%		155	%		151	%
Expected term (years)		1.73			3.24			3.29			3.73			4.96			1.98			3.49			3.54			3.98
Risk-free interest rate		0.48	%		0.95	%		0.96	%		1.07	%		1.36	%		0.67	%		1.23	%		1.25	%		1.37	%
Dividend yield		0.0	%		0.0	%		0.0	%		0.0	%		0.0	%		0.0	%		0.0	%		0.0	%		0.0	%
Exercise price	$	0.46		$	0.14		$	0.14		$	0.17		$	0.215		$	0.46		$	0.14		$	0.14		$	0.25
Common stock closing price	$	0.30		$	0.30		$	0.30		$	0.30		$	0.30		$	0.21		$	0.21		$	0.21		$	0.21

Warrant [Member]

Derivatives And Fair Value [Line Items]

Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block]

The following assumptions were used at March 31, 2015 and December 31, 2014:

	March 31, 2015			December 31, 2014
Volatility		96	%		91	%
Expected term (years)		1.00			1.25
Risk-free interest rate		0.26	%		0.36	%
Dividend yield		0.0	%		0.0	%
Exercise price	$	0.14		$	0.14
Common stock closing price	$	0.30		$	0.21