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COMMON UNIT-BASED COMPENSATION PLANS - SERP and Directors Comp (Details) - SERP and Deferred Compensation Plans - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Other information        
Unit-based compensation expense $ 400 $ 700 $ 1,600  
Total unit-based obligation recorded $ 13,500 $ 16,800    
Phantom Share Units (PSUs)        
Number of units        
Balance at the beginning of the period (in units) 760,630 631,365 635,837  
Granted (in units) 46,638 129,265 111,012  
Issued (in units) (138,570)   (115,484) [1]  
Balance at the end of the period (in units) 668,698 760,630 631,365  
Weighted average grant date fair value per unit        
Balance at the beginning of the period (in dollars per unit) $ 22.04 $ 25.48 $ 27.34  
Granted (in dollars per unit) 9.45 5.25 14.50  
Issued (in dollars per unit) 25.86   25.20 [1]  
Balance at the end of the period (in dollars per unit) $ 20.13 $ 22.04 $ 25.48  
Intrinsic value of outstanding grants (in dollars) $ 8,452 $ 3,408 $ 6,831 $ 11,025
Other information        
Common units issued 102,962   115,484  
[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.