Table:
|  | Number of shares | Weighted-average grant date fair value |
| --- | --- | --- |
| Nonvested at December 31, 2017 | 0.859 | $ 187.01 |
| Granted | 0.410 | 278.29 |
| Vested | (0.492) | 204.24 |
| Forfeited | (0.038) | 191.51 |
| Nonvested at December 31, 2018 | 0.739 | $ 225.93 |
| Granted | 0.321 | 318.75 |
| Vested | (0.290) | 209.05 |
| Forfeited | (0.061) | 225.23 |
| Nonvested at December 31, 2019 | 0.709 | $ 275.00 |
Paragraphs:
Restricted Stock Grants—During 2019 and 2018, the Company granted 0.321 and 0.410 shares, respectively, of restricted stock to certain employee and director participants under its share-based compensation plans. Restricted stock grants generally vest over a period of 1 to 4 years. The Company recorded $72.5, $109.7 and $63.0 of compensation expense related to outstanding shares of restricted stock held by employees and directors during 2019, 2018 and 2017, respectively. In 2018, this expense included $29.4 associated with accelerated vesting due to the passing of our former executive chairman. A summary of the Company’s nonvested shares activity for 2019 and 2018 is as follows:
At December 31, 2019, there was $77.9 of total unrecognized compensation expense related to nonvested awards granted to both employees and directors under the Company’s share-based compensation plans. That cost is expected to be recognized over a weighted-average period of 1.8 years. Unrecognized compensation expense related to nonvested shares of restricted stock grants is recorded as a reduction to additional paid-in capital in stockholder’s equity at December 31, 2019.
Employee Stock Purchase Plan—During 2019, 2018 and 2017, participants of the ESPP purchased 0.021, 0.020 and 0.020 shares, respectively, of Roper’s common stock for total consideration of $6.8, $5.4, and $4.2, respectively. All of these shares were purchased from Roper’s treasury shares.
Question:
How long does restricted stock grants generally vest over?
Answer: a period of 1 to 4 years