Stock Based Compensation - Restricted Stock and Stock Options (Details) - USD ($)
$ / shares in Units, $ in Thousands |
3 Months Ended |
9 Months Ended |
12 Months Ended |
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Changes in unvested restricted stock |
|
|
|
|
|
|
| Unvested restricted common stock, beginning of period (in shares) |
|
|
1,596,853
|
|
|
|
| Vested (in shares) |
|
|
(580,662)
|
|
|
|
| Unvested restricted common stock, end of period(in shares) |
1,016,191
|
|
1,016,191
|
|
1,596,853
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
|
| Balance, beginning of period |
|
|
$ 0.0188
|
|
|
|
| Vested (in dollars per share) |
|
|
0.0162
|
|
|
|
| Balance, beginning of period |
$ 0.0203
|
|
$ 0.0203
|
|
$ 0.0188
|
|
| Compensation expense |
$ 3,691
|
$ 1,057
|
$ 13,099
|
$ 1,562
|
|
|
| Changes in unvested stock options |
|
|
|
|
|
|
| Options exercised prior to vesting (in shares) |
|
|
|
|
|
75,304
|
| Options exercised prior to vesting , exercise price per share |
|
|
|
|
|
$ 0.03
|
| Unvested stock options (in shares) |
26,301
|
|
26,301
|
|
39,338
|
|
| Outstanding, beginning of period (in shares) |
|
|
1,713,385
|
|
|
|
| Granted (in shares) |
|
|
1,450,441
|
|
|
|
| Exercised (in shares) |
|
|
(60,357)
|
|
|
|
| Cancelled (in shares) |
|
|
(12,659)
|
|
|
|
| Outstanding, end of period (in shares) |
3,090,810
|
|
3,090,810
|
|
1,713,385
|
|
| Vested and expected to vest (in shares) |
3,040,552
|
|
3,040,552
|
|
|
|
| Exercisable (in shares) |
362,474
|
|
362,474
|
|
|
|
| Outstanding, beginning of period (in dollars per share) |
|
|
$ 6.31
|
|
|
|
| Granted (in dollars per share) |
|
|
21.36
|
|
|
|
| Exercised (in dollars per share) |
|
|
3.47
|
|
|
|
| Cancelled (in dollars per share) |
|
|
9.71
|
|
|
|
| Outstanding, end of period (in dollars per share) |
$ 13.41
|
|
13.41
|
|
$ 6.31
|
|
| Vested and expected to vest outstanding, weighted average exercise price (in dollars per share) |
13.41
|
|
13.41
|
|
|
|
| Exercisable (in dollar per share) |
$ 5.20
|
|
$ 5.20
|
|
|
|
| Remaining contractual life |
|
|
9 years 1 month 6 days
|
|
9 years 7 months 6 days
|
|
| Vested and expected to vest, remaining contractual life |
|
|
9 years 1 month 6 days
|
|
|
|
| Exercisable, remaining contractual life |
|
|
8 years 9 months 18 days
|
|
|
|
| Aggregate intrinsic value |
$ 11,639
|
|
$ 11,639
|
|
$ 15,580
|
|
| Vesting and expected to vest, aggregate intrinsic value |
11,449
|
|
11,449
|
|
|
|
| Exercisable, aggregated intrinsic value |
$ 3,055
|
|
3,055
|
|
|
|
| Employees and directors |
|
|
|
|
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
|
| Compensation expense |
|
|
$ 4,000
|
$ 300
|
|
|
| Changes in unvested stock options |
|
|
|
|
|
|
| Weighted average fair value of options granted (per share) |
$ 15.01
|
$ 4.71
|
$ 15.01
|
$ 4.71
|
|
|
| Employees |
|
|
|
|
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
|
| Unrecognized stock-based compensation expense |
$ 22,800
|
|
$ 22,800
|
|
|
|
| Period for recognition |
|
|
3 years
|
|
|
|
| Restricted Stock | Employees |
|
|
|
|
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
|
| Compensation expense |
|
|
$ 0
|
$ 0
|
|
|
| Unrecognized stock-based compensation expense |
0
|
|
0
|
|
|
|
| Restricted Stock | Non-employees |
|
|
|
|
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
|
| Compensation expense |
|
|
7,000
|
$ 1,200
|
|
|
| Unrecognized stock-based compensation expense |
$ 4,100
|
|
$ 4,100
|
|
|
|
| Period for recognition |
|
|
9 months 18 days
|
|
|
|