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Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the consolidated balance sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in thousands).

	Twelve Months Ended December 31, 2018				Twelve Months Ended December 31, 2017				Twelve Months Ended December 31, 2016
	Beginning of period		End of period		Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	69,418	$	134,758	$	163,620	$	69,418	$	102,138	$	163,620
Restricted cash		2,475		4,826		2,375		2,475		375		2,375
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	71,893	$	139,584	$	165,995	$	71,893	$	102,513	$	165,995

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,
	2018			2017			2016
Stock Options:
Expected volatility		71	%		68	%		78	%
Risk-free interest rate		3	%		2	%	1-2%
Expected dividend yield		0	%		0	%		0	%
Expected life of options in years		5.7			5.8			5.7

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

	Years Ended December 31,
	2018			2017			2016
Employee Stock Purchase Plan:
Expected volatility	59%-79%			44%-62%			60%-77%
Risk-free interest rate	2.1%-2.8%			1.0%-1.7%			0.4%-1.0%
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,
	2018		2017		2016
Cost of product sales	$	3,863	$	3,690	$	1,218
Research and development		32,038		26,485		18,050
Sales, general and administrative		45,663		45,357		35,997
	$	81,564	$	75,532	$	55,265