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LONG-TERM INCENTIVE AND RETIREMENT PLANS - Long-Term Incentive Plan and Unit Appreciation Right Activity (Detail) - shares
3 Months Ended 12 Months Ended
Sep. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted phantom units | 2018 Plan        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Outstanding, beginning of period (in shares)     108,602 117,630
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in Period     354,104 41,732
Settled in common units or cash (in shares)     (709) (16,098)
Forfeiture (in shares)     (87,536)  
Performance vesting forfeiture (in shares)     (29,512) (34,662)
Outstanding, end of period (in shares)     344,949 108,602
Restricted phantom units | 2004 Plan        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Outstanding, beginning of period (in shares)     219,306 205,510
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in Period     0 13,796
Settled in common units or cash (in shares)     0 0
Outstanding, end of period (in shares)     219,306 219,306
Restricted Units        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in Period 31,607 31,295    
Settled in common units or cash (in shares) (49,379) (48,924)    
Performance vesting forfeiture (in shares) (17,772) (17,629)    
Restricted Units | 2018 Plan        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Outstanding, beginning of period (in shares)     0 0
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in Period     780,949 0
Settled in common units or cash (in shares)     0 0
Performance vesting forfeiture (in shares)     0 0
Outstanding, end of period (in shares)     780,949 0
Unit appreciation rights        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]        
Outstanding, beginning of period (in shares)     58,646 66,355
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in Period     0 0
Performance vesting forfeiture (in shares)     (43,646) (7,709)
Outstanding, end of period (in shares)     15,000 58,646
Exercised (in shares)     0 0
Exercisable, end of period (in shares)     15,000 57,081