| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | Period [Axis] |
|---|
2016-01-01 - 2016-12-31 |
|---|
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | |
Summary of Activity under ESPP |
Activity under the ESPP for the years ended December 31, was as follows:
|
|
|
|
|
Number of shares purchased |
|
|
Purchase price |
|
|
2016 |
|
|
2015 |
|
|
2014 |
|
|
$ |
8.50 |
|
|
|
63,291 |
|
|
|
89,440 |
|
|
|
32,101 |
|
|
$ |
13.87 |
|
|
|
2,865 |
|
|
|
2,540 |
|
|
|
— |
|
|
$ |
20.02 |
|
|
|
30,389 |
|
|
|
— |
|
|
|
— |
|
|
$ |
25.56 |
|
|
|
5,158 |
|
|
|
— |
|
|
|
— |
|
|
$ |
36.14 |
|
|
|
— |
|
|
|
1,253 |
|
|
|
— |
|
|
|
|
|
|
|
101,703 |
|
|
|
93,233 |
|
|
|
32,101 |
|
|
Weighted Average Assumptions used to Determine Fair Value of Stock Awards |
In determining the fair value of stock awards granted, the following weighted average assumptions were used in the Black-Scholes option pricing model for awards granted in the periods indicated:
|
|
|
Stock Options |
|
|
Employee Stock Purchase Plan |
|
|
|
|
|
Years Ended |
|
|
Year Ended |
|
|
|
|
|
December 31, |
|
|
December 31, |
|
|
|
|
|
2016 |
|
|
2015 |
|
|
2014 |
|
|
2016 |
|
|
2015 |
|
|
2014 |
|
|
|
Volatility |
|
|
60.5% |
|
|
|
59.5% |
|
|
|
66.1% |
|
|
|
68.0% |
|
|
|
57.0% |
|
|
|
59.1% |
|
|
|
Expected term (years) |
|
|
6.1 |
|
|
|
6.1 |
|
|
|
6.1 |
|
|
|
1.4 |
|
|
|
0.9 |
|
|
|
0.6 |
|
|
|
Risk-free interest rate |
|
|
1.4% |
|
|
|
1.6% |
|
|
|
1.9% |
|
|
|
0.8% |
|
|
|
0.3% |
|
|
|
0.1% |
|
|
|
Dividend rate |
|
|
0.0% |
|
|
|
0.0% |
|
|
|
0.0% |
|
|
|
0.0% |
|
|
|
0.0% |
|
|
|
0.0% |
|
|
|
Stock Based Compensation Expense |
The following table presents stock-based compensation expense included in the Company’s consolidated statements of operations:
|
|
|
Years Ended |
|
|
|
|
December 31, |
|
|
|
|
2016 |
|
|
2015 |
|
|
2014 |
|
|
|
|
(in thousands) |
|
|
Research and development |
|
$ |
7,578 |
|
|
$ |
3,449 |
|
|
$ |
701 |
|
|
General and administrative |
|
|
6,379 |
|
|
|
2,690 |
|
|
|
549 |
|
|
|
|
$ |
13,957 |
|
|
$ |
6,139 |
|
|
$ |
1,250 |
|
|
Stock Option Activity |
A summary of the Company’s stock option activity and related information follows:
|
|
|
|
|
|
|
Weighted
average |
|
|
Weighted
average |
|
|
Aggregate |
|
|
|
|
|
|
|
|
exercise |
|
|
remaining contractual |
|
|
intrinsic value |
|
|
|
|
Shares |
|
|
price per share |
|
|
life (years) |
|
|
(in thousands) |
|
|
Options, Outstanding at beginning of period |
|
|
2,961,107 |
|
|
$ |
14.29 |
|
|
|
6.7 |
|
|
$ |
57,281 |
|
|
Granted |
|
|
2,362,075 |
|
|
|
25.95 |
|
|
|
|
|
|
|
|
|
|
Exercised |
|
|
(376,919 |
) |
|
|
2.44 |
|
|
|
|
|
|
|
|
|
|
Forfeited and expired |
|
|
(28,211 |
) |
|
|
28.44 |
|
|
|
|
|
|
|
|
|
|
Options, Outstanding at end of period |
|
|
4,918,052 |
|
|
$ |
20.72 |
|
|
|
7.8 |
|
|
$ |
23,098 |
|
|
Exercisable at December 31, 2016 |
|
|
1,800,362 |
|
|
$ |
11.43 |
|
|
|
5.6 |
|
|
$ |
21,310 |
|
|
Vested and expected to vest at December 31, 2016 |
|
|
4,843,599 |
|
|
$ |
20.62 |
|
|
|
7.8 |
|
|
$ |
23,087 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Summary of Stock Option Value |
The following table summarizes the Company’s stock option values:
|
|
|
Years Ended |
|
|
|
|
December 31, |
|
|
|
|
2016 |
|
|
2015 |
|
|
2014 |
|
|
|
|
(in thousands, except per share data) |
|
|
Weighted average fair value of option shares granted
during the period |
|
$ |
14.63 |
|
|
$ |
17.43 |
|
|
$ |
7.25 |
|
|
Total intrinsic value of stock options exercised |
|
|
10,179 |
|
|
|
20,389 |
|
|
|
2,590 |
|
|
Total fair value of stock options vested |
|
|
9,207 |
|
|
|
2,133 |
|
|
|
683 |
|
|