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Stock Based Compensation (Tables)

6 Months Ended

Jun. 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 six months ended June 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		1,392,841		$	35.41
Options exercised		(736,163	)	$	9.51
Options canceled		(108,928	)	$	25.95
Balance at June 30, 2015		4,796,918		$	21.21

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 June 30,						Six Month Ended June 30,
	2015			2014			2015			2014
Risk-free interest rate		1.85	%		1.89	%		1.70	%		1.89	%
Expected life	6.0 years			5.8 years			6.0 years			5.9 years
Expected volatility		64	%		80	%		65	%		80	%
Dividend yield	—			—			—			—

Summary of Restricted Stock Units (RSUs) Activity

The following table summarizes restricted stock units (RSUs) activity under our 2013 Equity Incentive Plan and related information during the six months ended June 30, 2015:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	RSUs			fair value per share
Balance at December 31, 2014		—		$	—
RSUs granted		182,825		$	30.22
RSUs exercised		—		$	—
RSUs canceled		(9,250	)	$	29.72
Balance at June 30, 2015		173,575		$	30.24

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

	Six Month Ended June 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 June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Research and development	$	2,542	$	1,283	$	4,751	$	2,330
Selling, general and administrative		2,216		1,140		5,180		2,396
Total stock-based compensation	$	4,758	$	2,423	$	9,931	$	4,726