| Share-based Compensation Arrangements |
The following table summarizes stock-based compensation expense: | | | | | | | | | | | | | Years Ended December 31, | | 2020 | | 2019 | | Stock options | $ | 792,055 | | | $ | 1,542,644 | | | Restricted stock | 3,228,750 | | | 437,354 | | | Total stock-based compensation expense | $ | 4,020,805 | | | $ | 1,979,998 | |
The following table summarizes stock option activity: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Number of Options | | Weighted
Average
Exercise Price
per Option | | Weighted
Average Grant
Date Fair Value
per Option | | Weighted
Average
Remaining Contractual Life (Years) | | Balance, December 31, 2018 | | 3,867,621 | | | $ | 4.1 | | | | | | | Granted | | 2,450,000 | | | 1.0 | | | 0.5 | | | | | Exercised | | (736,552) | | | 0.7 | | | | | | | Forfeited | | (907,500) | | | 4.5 | | | | | | | Expired | | (948,569) | | | 5.0 | | | | | | | Balance, December 31, 2019 | | 3,725,000 | | | 2.3 | | | | | | | Granted | | 877,575 | | | 1.9 | | | 0.6 | | | | | Exercised | | (2,112,392) | | | 2.4 | | | | | | | Forfeited | | (118,943) | | | 5.8 | | | | | | | Expired | | (20,000) | | | 2.4 | | | | | | | Balance, December 31, 2020 | | 2,351,240 | | | $ | 2.0 | | | | | 5.5 | | | | | | | | | | | Number of options exercisable at December 31, 2020 | | 1,972,740 | | | $ | 2.1 | | | | | 5.8 |
The following table summarizes restricted stock activity: | | | | | | | | | | | | | | | | | Number of Unvested Shares | | Weighted Average Grant Date Fair Value per Share | | Balance, December 31, 2018 | | — | | | $ | — | | | Granted | | 1,805,222 | | | 2.6 | | | Vested | | (36,496) | | | 2.7 | | | Forfeited | | — | | | — | | | Balance, December 31, 2019 | | 1,768,726 | | | 2.6 | | | Granted | | 657,135 | | | 2.9 | | | Vested | | (1,047,972) | | | 2.6 | | | Forfeited | | — | | | — | | | Balance, December 31, 2020 | | 1,377,889 | | | $ | 2.7 | |
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