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Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

The following table summarizes option activity under our 2013 Equity Incentive Plan and related information during the nine months ended September 30, 2015:

	Shares
	Subject to			Weighted-
	Outstanding			Average Exercise
	Options			Price Per Share
Balance at December 31, 2014		4,249,168		$	14.77
Options granted		1,649,691		$	37.32
Options exercised		(1,034,140	)	$	9.58
Options canceled		(152,365	)	$	28.13
Balance at September 30, 2015		4,712,354		$	23.25

Fair Values of Employee Stock Options

The estimated grant date fair values of the employee stock options were calculated using the Black Scholes valuation model, based on the following assumptions:

	Three Month Ended September 30,						Nine Month Ended September 30,
	2015			2014			2015			2014
Risk-free interest rate		1.77	%		1.89	%		1.65	%		1.89	%
Expected life	6.0 years			5.8 years			6.0 years			5.9 years
Expected volatility		65	%		79	%		65	%		80	%
Dividend yield	—			—			—			—

Summary of Restricted Stock Units (RSUs) Activity Including Performance-Based RSUs

The following table summarizes restricted stock units (RSUs) activity, including performance-based RSUs activity, under our 2013 Equity Incentive Plan and related information during the nine months ended September 30, 2015:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	RSUs			fair value per share
Balance at December 31, 2014		—		$	—
RSUs granted		203,258		$	32.14
RSUs exercised		—		$	—
RSUs canceled		(11,485	)	$	30.12
Balance at September 30, 2015		191,773		$	32.26

Assumptions used to Determine Weighted-Average Fair Value of Performance Stock Units

	Nine Month Ended September 30, 2015
	PSUs
Number of PSUs granted		165,000
Weighted-average grant date stock price	$	31.95
Weighted-average risk-free interest rate		1.13	%
Weighted-average volatility		62	%
Dividend yield	—
Weighted- average fair value per share of PSUs granted ($50 Vesting Hurdle)	$	25.65
Weighted- average fair value per share of PSUs granted ($60 Vesting Hurdle)	$	23.24

Classification of Stock-Based Compensation Expense

The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Research and development	$	3,252	$	953	$	8,004	$	3,321
Selling, general and administrative		2,849		1,197		8,028		3,555
Total stock-based compensation	$	6,101	$	2,150	$	16,032	$	6,876