Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

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

Weighted-Average Assumptions Used to Estimate Fair Value of Employee Stock Options

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

	Years Ended December 31,
	2017			2016			2015
Stock Options:
Expected volatility		68	%		78	%		89	%
Risk-free interest rate		2	%	1-2		%		1-2	%
Expected dividend yield		0	%		0	%		0	%
Expected life of options in years		5.8			5.7			5.7

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

	Years Ended December 31,
	2017			2016			2015
Employee Stock Purchase Plan:
Expected volatility	44%-62		%	60%-77		%	51%-59		%
Risk-free interest rate	1.0%-1.7		%	0.4%-1.0		%	0.1%-0.9		%
Expected dividend yield		0	%		0	%		0	%
Expected life in years	0.5-2.0			0.5-2.0			0.5-2.0

Summary of Stock-based Compensation Expense Included in Statements of Operations

The table below summarizes the total stock-based compensation expense included in the Company’s statements of operations for the periods presented (in thousands):

	Years Ended December 31,
	2017		2016		2015
Cost of product sales	$	3,690	$	1,218	$	—
Research and development		26,485		18,050		12,171
Sales, general and administrative		45,357		35,997		28,023
	$	75,532	$	55,265	$	40,194