Equity Plans and Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Option Activity under Stock-Based Compensation Plans

Option activity under our stock-based compensation plans during the six months ended June 30, 2015 was as follows (in thousands except per share amounts):

	Shares Underlying Outstanding Options (in thousands)			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2014		1,820		$	27.48
Options granted		1,094			16.83
Options exercised		(8	)		15.60
Options cancelled:
Options forfeited (unvested)		(82	)		17.34
Options cancelled (vested)		(101	)		43.55
Balance at June 30, 2015		2,723			22.92		7.23	$	12,303
Vested and expected to vest at June 30, 2015		2,568			23.27		7.10	$	11,323
Exercisable at June 30, 2015		1,166			29.61		4.64	$	3,001

Summary of Restricted Stock Units Activity

Restricted stock unit activity under our stock-based compensation plans during the six months ended June 30, 2015 was as follows (in thousands except per share amounts):

	Number of Shares (In thousands)			Weighted-Average Grant-Date Fair Value
Non-vested as of December 31, 2014		179		$	17.13
Granted		24		$	16.16
Vested		(3	)	$	16.90
Forfeited or expired		(5	)	$	18.71
Non-vested as of June 30, 2015		195		$	16.97

Fair Value-Based Measurements and Weighted-Average Assumptions

The fair value-based measurements and weighted-average assumptions used in the calculations of these measurements are as follows:

	Stock Options						Stock Options						Employee Stock Purchase Plan
	Three Months Ended						Six Months Ended						Six Months Ended
	June 30,						June 30,						June 30,
	2015			2014			2015			2014			2015			2014
Weighted-average fair value	$	14.28		$	13.60		$	12.76		$	15.50		$	8.18		$	9.20
Risk-free interest rate		1.7	%		1.9	%		1.7	%		1.8	%		0.4	%		0.2	%
Expected life (in years)		5.9			5.8			5.9			5.9			1.2			1.1
Volatility		0.7			1.3			0.7			1.4			0.7			0.9

Stock-Based Compensation Expense

The components of stock-based compensation expense were (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2015		2014		2015		2014
Research and development	$	868	$	738	$	1,753	$	1,430
General and administrative		1,050		938		2,119		1,516
Total	$	1,918	$	1,676	$	3,872	$	2,946