Table:
|  |  | Years Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Employee stock options | $219 | $438 | $1,980 |
| Restricted stock awards and units | 29,031 | 27,974 | 28,909 |
| Employee stock purchase plan | 2,304 | 2,599 | 2,573 |
| Total stock-based compensation expense | $31,554 | $31,011 | $33,462 |
Paragraphs:
Stock-based compensation expense categorized by various equity components for the years ended December 31, 2019, 2018 and 2017 is summarized in the table below (in thousands):
During the years ended December 31, 2019, 2018 and 2017, the Company granted stock options covering zero, zero and 70,000 shares, respectively. The 2017 estimated per share fair value of the grant was $4.62 before estimated forfeitures.
The total fair value of restricted stock awards and units vested during the years ended December 31, 2019, 2018 and 2017 was $30.1 million, $30.4 million and $22.7 million, respectively.
The total intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $0.2 million, $1.0 million and $5.5 million, respectively. The intrinsic value is calculated as the difference between the market value on the date of exercise and the exercise price of the shares.
As of December 31, 2019, the unrecognized stock-based compensation balance after estimated forfeitures consisted of $0.1 million related to unvested stock options, to be recognized over an estimated weighted average amortization period of 1.5 years, and $40.3 million related to restricted stock awards and units, including performance-based awards and units, to be recognized over an estimated weighted average amortization period of 2.3 years.
As of December 31, 2018, the unrecognized stock-based compensation balance after estimated forfeitures related to unvested stock options was $0.3 million to be recognized over an estimated weighted average amortization period of 2.0 years and $40.6 million related to restricted stock awards and units, including performance-based awards and units, to be recognized over an estimated weighted average amortization period of 2.2 years.
Question:
How does the company calculate the intrinsic value?
Answer: the difference between the market value on the date of exercise and the exercise price of the shares