Stock‑Based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Stock-Based Compensation

Summary of stock option activity

	Outstanding Options
					Weighted‑
			Weighted‑		Average
	Shares		Average		Remaining	Aggregate
	Available for	Number of	Exercise		Contractual	Intrinsic
(in thousands, except for contractual life and exercise price)	Grant	Shares	Price		Life	Value
					(In years)
Balance at December 31, 2014	294	8,463	$	2.28	8.83
Additional shares authorized	1,534
Options granted	(1,465)	1,465		8.96
Options exercised	—	(179)		1.71
Options forfeited	346	(346)		3.26
Balance at June 30, 2015	709	9,403		3.30	8.66	137,066
Exercisable at June 30, 2015		5,390		1.65	5.72	87,708
Vested and expected to vest at June 30, 2015		8,443		3.08	8.32	124,597

Summary of stock-based compensation expenses

	Three months ended  June 30,
	2015						2014
	Employee		Non‑Employee		Total		Employee		Non‑Employee		Total
	(in thousands)
Cost of revenues	$	88	$	184	$	272	$	32	$	1	$	33
Research and development		309		11		320		94		3		97
Selling, general and administrative		926		74		1,000		282		6		288
Total	$	1,323	$	269	$	1,592	$	408	$	10	$	418

	Six months ended June 30,
	2015						2014
	Employee		Non‑Employee		Total		Employee		Non‑Employee		Total
	(in thousands)
Cost of revenues	$	149	$	206	$	355	$	97	$	4	$	101
Research and development		558		23		581		1,143		7		1,150
Selling, general and administrative		1,711		93		1,804		1,764		13		1,777
Total	$	2,418	$	322	$	2,740	$	3,004	$	24	$	3,028

Schedule of assumptions used in valuation of fair value of employee stock options

	Three months ended							Six months ended
	June 30,							June 30,
	2015					2014		2015					2014
Expected term	5.9		—	6.1			—	5.6		—	6.1		5.4		—	6.3
Expected volatility	72.0	%	—	73.0	%		—	72.0	%	—	73.0	%	84.4	%	—	87.0	%
Expected dividend rate				0	%		—				0	%				0	%
Risk‑free interest rate	1.84	%	—	1.88	%		—	1.56	%	—	1.88	%	1.65	%	—	1.94	%