PARTNERS' CAPITAL - Change (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		26 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ 1,067,504	$ 1,265,424	$ 1,388,109	$ 1,187,687	$ 1,265,424	$ 1,187,687
Balance at beginning of period (in units)		126,915,597			126,915,597
Comprehensive income (loss):
Net income (loss)	(46,679)	$ (144,707)	58,184	283,604	$ (191,386)	341,788
Actuarially determined long-term liability adjustments	939	938	(118)	(3,584)	1,877	(3,702)
COMPREHENSIVE INCOME (LOSS)	(45,740)	(143,769)	58,066	280,020	(189,509)	338,086
Settlement of deferred compensation plans		(1,310)		(7,817)
Purchase of units under unit repurchase program				(5,251)			$ (93,500)
Common unit-based compensation	1,610	(527)	3,021	2,743
Distributions on deferred common unit-based compensation		(986)	(799)	(1,280)
Distributions from consolidated company to noncontrolling interest	(222)	(288)	(228)	(262)
Distributions to Partners		(50,767)	(68,690)	(67,731)
Other		(273)
Balance at end of period	$ 1,023,152	1,067,504	1,379,479	1,388,109	$ 1,023,152	1,379,479	$ 1,023,152
Balance at end of period (in units)	127,195,219				127,195,219		127,195,219
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ (77,055)	(77,993)	(50,455)	(46,871)	$ (77,993)	(46,871)
Comprehensive income (loss):
Actuarially determined long-term liability adjustments	939	938	(118)	(3,584)
Balance at end of period	(76,116)	(77,055)	(50,573)	(50,455)	(76,116)	(50,573)	$ (76,116)
Noncontrolling Interest
Increase (Decrease) in Partners's Capital
Balance at beginning of period	11,723	11,935	12,204	5,290	11,935	5,290
Comprehensive income (loss):
Net income (loss)	(15)	76	114	7,176
Distributions from consolidated company to noncontrolling interest	(222)	(288)	(228)	(262)
Balance at end of period	11,486	11,723	12,090	12,204	11,486	12,090	11,486
Limited Partners' Capital
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ 1,132,836	$ 1,331,482	$ 1,426,360	$ 1,229,268	$ 1,331,482	$ 1,229,268
Balance at beginning of period (in units)	127,195,219	126,915,597	128,391,191	128,095,511	126,915,597	128,095,511
Comprehensive income (loss):
Net income (loss)	$ (46,664)	$ (144,783)	$ 58,070	$ 276,428
Settlement of deferred compensation plans		$ (1,310)		$ (7,817)
Settlement of deferred compensation plans (in units)		279,622		596,650
Purchase of units under unit repurchase program				$ (5,251)
Purchase of units under unit repurchase program (in units)				(300,970)
Common unit-based compensation	1,610	$ (527)	3,021	$ 2,743
Distributions on deferred common unit-based compensation		(986)	(799)	(1,280)
Distributions to Partners		(50,767)	(68,690)	(67,731)
Other		(273)
Balance at end of period	$ 1,087,782	$ 1,132,836	$ 1,417,962	$ 1,426,360	$ 1,087,782	$ 1,417,962	$ 1,087,782
Balance at end of period (in units)	127,195,219	127,195,219	128,391,191	128,391,191	127,195,219	128,391,191	127,195,219