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COMMON UNIT-BASED COMPENSATION PLANS (Tables) | 12 Months Ended
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Dec. 31, 2021
ARLP LTIP |
COMMON UNIT-BASED COMPENSATION PLANS |
Summary of activity in share-based plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Number of units |  | Weighted average grant date fair value per unit |  | Intrinsic value |
​ | ​ | ​ | ​ | ​ | ​ | ​ | (in thousands) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Non-vested grants at January 1, 2019 | ​ | 1,828,080 | ​ | $ | 17.18 | ​ | $ | 31,699 | ​
Granted | ​ | 682,155 | ​ | ​ | 18.63 | ​ | ​ | ​ | ​
Vested (1) | ​ | (885,381) | ​ |  | 12.38 | ​ | ​ | ​ | ​
Forfeited | ​ | (21,476) | ​ |  | 20.84 | ​ | ​ | ​ | ​
Non-vested grants at December 31, 2019 | ​ | 1,603,378 | ​ | ​ | 20.39 | ​ | ​ | 17,349 | ​
Granted (2) | ​ | 1,430,489 | ​ | ​ | 5.02 | ​ | ​ | ​ | ​
Vested (3) | ​ | (919,524) | ​ | ​ | 21.70 | ​ | ​ | ​ | ​
Grants canceled (4) | ​ | (675,302) | ​ |  | 18.62 | ​ | ​ | ​ | ​
Forfeited | ​ | (8,552) | ​ |  | 20.16 | ​ | ​ | ​ | ​
Non-vested grants at December 31, 2020 | ​ | 1,430,489 | ​ | ​ | 5.02 | ​ | ​ | 6,409 | ​
Granted (5) |  | 1,818,190 | ​ | ​ | 6.03 | ​ | ​ | ​ | ​
Forfeited |  | (118,204) | ​ |  | 5.48 | ​ | ​ | ​ | ​
Non-vested grants at December 31, 2021 |  | 3,130,475 | ​ |  | 5.59 | ​ | ​ | 39,569 | ​
(1) | During the year ended December 31, 2019, we issued 596,650 unrestricted common units to LTIP participants. The remaining vested units were settled in cash to satisfy tax withholding obligations of the LTIP participants.
(2) | In December 2020, we modified the vesting requirements for certain restricted units that we granted in February 2020 which were determined to be improbable of vesting under the original vesting requirements (the "2020 Grants"). The new vesting requirements make it probable the modified restricted units will vest. Also in December 2020, an additional 578,114 restricted units under these modified vesting requirements were granted. The grant date fair value reflects the modification date fair value for those awards that were modified.
(3) | In February 2020, we issued 279,622 unrestricted common units to LTIP participants as a result of satisfying the vesting requirements for 424,486 restricted units that were granted in 2017. The remaining vested units were settled in cash to satisfy tax withholding obligations of the LTIP participants. In December 2020, we accelerated the vesting requirements for 495,038 restricted units that were granted in 2018 (the "2018 Grants") and settled these restricted units in cash.
(4) | In December 2020, 675,302 restricted units that were granted in 2019 (the "2019 Grants") were canceled since it was determined that the vesting requirements for these restricted units were not probable of being satisfied.
(5) | In April 2021, we granted 921,430 restricted units and 896,760 restricted units that have minimum-value guarantees of $2.53 per unit and $3.79 per unit, respectively, regardless of whether or not the awards vest.
SERP and Deferred Compensation Plans |
COMMON UNIT-BASED COMPENSATION PLANS |
Summary of activity in share-based plans |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Number of units |  | Weighted average grant date fair value per unit |  | Intrinsic value |
​ | ​ | ​ | ​ | ​ | ​ | ​ | (in thousands) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Phantom units outstanding as of January 1, 2019 | ​ | 635,837 | ​ | $ | 27.34 | ​ | $ | 11,025 | ​
Granted | ​ | 111,012 | ​ | ​ | 14.50 | ​ | ​ | ​ | ​
Issued (1) | ​ | (115,484) | ​ | ​ | 25.20 | ​ | ​ | ​ | ​
Phantom units outstanding as of December 31, 2019 | ​ | 631,365 | ​ | ​ | 25.48 | ​ | ​ | 6,831 | ​
Granted | ​ | 129,265 | ​ | ​ | 5.25 | ​ | ​ | ​ | ​
Phantom units outstanding as of December 31, 2020 | ​ | 760,630 | ​ | ​ | 22.04 | ​ | ​ | 3,408 | ​
Granted | ​ | 46,638 | ​ | ​ | 9.45 | ​ | ​ | ​ | ​
Issued (1) |  | (138,570) | ​ | ​ | 25.86 | ​ | ​ | ​ | ​
Phantom units outstanding as of December 31, 2021 |  | 668,698 | ​ |  | 20.13 | ​ | ​ | 8,452 | ​
(1) | During the years ended December 31, 2021 and 2019, we issued ARLP common units that we purchased on the open market of 102,962 and 115,484, respectively, to participants under the SERP and Directors' Deferred Compensation Plan. Units issued in 2021 were net of units settled in cash to satisfy tax withholding obligations.

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