Stock-Based Compensation - Stock option activity and fair value of stock option grants(Details) - Stock Options - USD ($)
|
12 Months Ended |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Options |
|
|
|
| Outstanding beginning of period (in shares) |
1,629,342
|
|
|
| Options granted (in shares) |
24,000
|
|
|
| Options exercised (in shares) |
(111,763)
|
|
|
| Options cancelled (in shares) |
(59,375)
|
|
|
| Outstanding end of period (in shares) |
1,482,204
|
1,629,342
|
|
| Exercisable (in shares) |
1,200,199
|
|
|
| Weighted-Average Exercise Price Per Share |
|
|
|
| Outstanding beginning of period (in dollars per share) |
$ 2.58
|
|
|
| Options granted (in dollars per share) |
21.78
|
|
|
| Options exercised (in dollars per share) |
1.85
|
|
|
| Options canceled (in dollars per share) |
8.60
|
|
|
| Outstanding end of period (in dollars per share) |
2.70
|
$ 2.58
|
|
| Exercisable (in dollars per share) |
$ 1.85
|
|
|
| Weighted-Average Remaining Contractual Life (Yrs) |
|
|
|
| Weighted-Average Remaining Contractual Life, Outstanding (in years) |
6 years 3 months 18 days
|
7 years 2 months 12 days
|
|
| Weighted-Average Remaining Contractual Life, Exercisable (in years) |
6 years
|
|
|
| Aggregate Intrinsic Value |
|
|
|
| Outstanding beginning of period (in dollars) |
$ 41,474,962
|
|
|
| Outstanding end of period (in dollars) |
12,788,462
|
$ 41,474,962
|
|
| Exercisable (in dollars) |
$ 11,151,738
|
|
|
| Weighted-average grant-date fair value of options granted (in dollars per share) |
$ 12.64
|
$ 11.75
|
$ 6.47
|
| Forfeiture rate (as a percent) |
1.00%
|
1.40%
|
3.00%
|
| Total unrecognized compensation expense |
$ 1,582,798
|
|
|
| Weighted average period expected to be recognized |
1 year 9 months 18 days
|
|
|
| Total grant date fair value of stock options vested during the period |
$ 1,300,021
|
|
|
| Total intrinsic value of options exercised |
$ 2,112,426
|
$ 6,954,526
|
$ 588,088
|
| Summary of weighted average assumptions used to estimate the fair value of stock option grants |
|
|
|
| Volatility (as a percent) |
61.50%
|
87.10%
|
104.30%
|
| Expected term (years) |
6 years 3 months 18 days
|
6 years 8 months 12 days
|
7 years
|
| Risk- free interest rate (as a percent) |
1.60%
|
1.80%
|
2.10%
|
| Dividend yield (as a percent) |
0.00%
|
0.00%
|
0.00%
|