Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Schedule of Estimated Useful Lives by Major Asset Category

Estimated useful lives by major asset category are as follows:

	Useful Lives
Machinery and equipment		5 to 7 years
Computers and software		3 years
Furniture and fixtures		10 years

Assumptions Used to Estimate Fair Value of Employee Stock Options

The estimated fair value of each stock option and purchase right, including the effect of estimated forfeitures, is then expensed over the requisite service period, which is generally the vesting period. The following assumptions were used during these periods:

	Years Ended December 31,
	2014			2013			2012
Stock Options:
Expected volatility		93	%		94	%		98-99	%
Risk-free interest rate		1-2	%		1-2	%		1	%
Expected dividend yield		0	%		0	%		0	%
Expected life of options in years		5.7			6.0			5.8-6.0

Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan Rights

	Years Ended December 31,
	2014			2013			2012
Employee Stock Purchase Plan:
Expected volatility		44-95	%		69-118	%		69-137	%
Risk-free interest rate		0.1-0.5	%		0.1-0.3	%		0.1-0.3	%
Expected dividend yield		0	%		0	%		0	%
Expected life of options in years		0.5-2.0			0.5-2.0			0.5-2.0

Potential Common Shares Excluded in Calculating Basic and Diluted Net Loss Per Common Share

Shares used in calculating basic and diluted net loss per common share exclude the following potential common shares as their effect is antidilutive (in thousands):

	Years Ended December 31,
	2014		2013		2012
Antidilutive options to purchase common stock		7,773		7,245		6,868
Antidilutive warrants to purchase common stock		1,966		3,116		4,388
		9,739		10,361		11,256