Stock plans - Risk free interest rate & Dividend yield (Details) - USD ($)
|
12 Months Ended |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Stock-based compensation |
$ 3,477,000
|
$ 971,000
|
$ 260,000
|
| ESPP |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected term (in years) |
6 months
|
|
|
| Expected volatility |
74.13%
|
|
|
| Risk-free interest rate |
0.33%
|
|
|
| Weighted-average grant date fair value (in dollars per share) |
$ 2.17
|
|
|
| Stock-based compensation |
$ 102,000
|
|
|
| Number of shares purchased |
0
|
|
|
| Cash received from payroll deductions |
$ 259,000
|
|
|
| Non Employees |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected volatility |
|
83.80%
|
88.50%
|
| Minimum | Non-Employee Options |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected volatility |
68.20%
|
83.80%
|
88.50%
|
| Risk-free interest rate |
1.28%
|
1.53%
|
0.99%
|
| Minimum | Non Employees |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected term (in years) |
7 years 3 months
|
9 years 4 months 13 days
|
9 years 3 months
|
| Expected volatility |
69.90%
|
|
|
| Risk-free interest rate |
1.86%
|
1.99%
|
2.85%
|
| Maximum | Non-Employee Options |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected term (in years) |
6 years 11 days
|
6 years 11 days
|
6 years 11 days
|
| Expected volatility |
79.70%
|
86.60%
|
94.50%
|
| Risk-free interest rate |
1.86%
|
1.91%
|
1.97%
|
| Maximum | Non Employees |
|
|
|
| Assumptions used in determination of fair value of options using the Black Scholes option pricing valuation model |
|
|
|
| Expected term (in years) |
9 years 9 months 26 days
|
9 years 4 months 24 days
|
9 years 7 months 6 days
|
| Expected volatility |
78.70%
|
|
|
| Risk-free interest rate |
2.25%
|
2.41%
|
2.94%
|