COMPENSATION PLANS - SERP and Directors Compensation Activity (Details) - SERP and Directors' Compensation Plans - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Other information
Unit-based compensation expense	$ 100	$ 400	$ 400	$ 700
Total unit-based obligation recorded	$ 16,300		$ 16,300
Phantom Share Units (PSUs)
Summary of units
Balance at the beginning of the period (in units)			631,365
Granted (in units)			29,544
Balance at the end of the period (in units)	660,909		660,909
Weighted average grant date fair value per unit
Balance at the beginning of the period (in dollars per unit)			$ 25.48
Granted (in dollars per unit)			7.87
Balance at the end of the period (in dollars per unit)	$ 24.69		$ 24.69
Intrinsic value (in dollars)
Intrinsic value of outstanding grants (in dollars)	$ 2,155		$ 2,155		$ 6,831