EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Deferred income taxes (a)		$ 2,910	$ (1,425)	$ (878)
Total recognized in other comprehensive income (loss)		(9,696)	4,771	(4,175)
Other Comprehensive Income (Loss), Risk-Management Assets/Liabilities of unconsolidated affiliates			2,424
Accumulated other comprehensive loss, net of tax		$ (131,481)	$ (121,785)	$ (105,411)
Expected long-term return on plan assets		7.50%	8.00%	7.75%
Compensation increase rate		3.65%	3.00%	3.10%
Defined Benefit Plan, Assumptions Used in Calculation (Long-term rate of return and discount rate)		We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We determine our discount rates annually utilizing portfolios of high quality bonds matched to the estimated benefit cash flows of our retirement and other postretirement benefit plans. Bonds selected to be included in the portfolios are only those rated by S&P or Moody’s as an AA or Aa2 rating or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds..
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligation		$ 534,849	$ 466,994	$ 481,615
Service cost		7,825	7,339	6,896
Interest cost		20,528	17,659	18,645
Plan participants’ contributions		0	0
Actuarial loss (gain)		55,954	(24,345)
Benefits paid		(16,452)	(15,274)
Fair value of plan assets		346,792	290,684	306,008
Actual return on plan assets		58,060	(12,350)
Employer contributions		14,500	12,300
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		0	0
Defined Benefit Plan, Plan Assets, Benefits Paid		16,452	15,274
Balance at December 31		(188,057)	(176,310)
Current liabilities		(4,616)	(4,514)
Noncurrent liabilities		(183,441)	(171,796)
Balance at December 31		(188,057)	(176,310)
Defined Benefit Plan, Accumulated Benefit Obligation		498,800	434,400
Expected return on plan assets		(23,600)	(23,917)	(21,376)
Amortization of prior service credit		0	0	0
Amortization of net loss		12,649	17,060	13,586
Net periodic benefit cost		17,402	18,141	17,751
Net gain (loss)		(25,389)	(16,351)	(16,572)
Prior service cost		(601)	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax		0	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		12,649	17,060	13,586
Deferred income taxes (a)		3,068	(18,928)	(960)
Total recognized in other comprehensive income (loss)		(10,273)	(18,219)	$ (3,946)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax		(601)	0
Accumulated loss		(172,952)	(160,212)
Accumulated other comprehensive loss		(173,553)	(160,212)
Deferred income taxes		46,354	43,286
Accumulated other comprehensive loss, net of tax		$ (127,199)	$ (116,926)
Discount rate		3.50%	4.50%
Compensation increase rate		3.70%	3.65%
Discount Rates - Retirement and Other Postretirement Plans		4.50%	3.75%	4.50%
Domestic and international equities		42.00%
Long duration fixed income		30.00%
Return-seeking credit		11.00%
Hedge funds		10.00%
Real estate funds		7.00%
Total		100.00%
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		$ 18,277
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		19,252
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		20,202
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		21,170
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		22,228
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		123,959
Retirement Plan [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 12,100
Retirement Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		110	$ 153
Retirement Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,263	3,961
Retirement Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,373	4,114
Retirement Plan [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		343,419	286,570
Retirement Plan [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		346,792	290,684
Retirement Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		47	58
Retirement Plan [Member] | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Equity securities | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		47	58
Retirement Plan [Member] | Equity securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		149,985	116,790
Retirement Plan [Member] | Equity securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		150,032	116,848
Retirement Plan [Member] | Real Estate Funds [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Real Estate Funds [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Real Estate Funds [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Real Estate Funds [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Real Estate Funds [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		23,885	20,569
Retirement Plan [Member] | Real Estate Funds [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		23,885	20,569
Retirement Plan [Member] | Government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Government obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Government obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		50,708	48,913
Retirement Plan [Member] | Government obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		50,708	48,913
Retirement Plan [Member] | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Corporate obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Corporate obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		85,898	69,377
Retirement Plan [Member] | Corporate obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		85,898	69,377
Retirement Plan [Member] | Common/collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Common/collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,263	3,961
Retirement Plan [Member] | Common/collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Common/collective trusts | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,263	3,961
Retirement Plan [Member] | Common/collective trusts | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Common/collective trusts | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,263	3,961
Retirement Plan [Member] | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			95
Retirement Plan [Member] | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0
Retirement Plan [Member] | Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0
Retirement Plan [Member] | Money market funds | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			95
Retirement Plan [Member] | Money market funds | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0
Retirement Plan [Member] | Money market funds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			95
Retirement Plan [Member] | Other Investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Other Investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Other Investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Other Investments | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Retirement Plan [Member] | Other Investments | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		32,943	30,921
Retirement Plan [Member] | Other Investments | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		32,943	30,921
Unfunded Capital Commitments		0	$ 0
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		63
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		63
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Retirement Plan [Member] | Cash and Cash Equivalents [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 63
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumed Health Care Cost Trend Rate		7.00%	6.50%
Defined Benefit Plan Assumed Ultimate Health Care Cost Trend Rate		5.00%	5.00%
Minimum Number Of Years Of Service For Certain Employees To Be Eligible To Participate In Welfare Plans That Provide Postretirement Medical And Life Insurance Benefits		5 years
Benefit Obligation		$ 52,309	$ 46,840	$ 57,938
Service cost		468	845	662
Interest cost		2,038	2,108	2,261
Plan participants’ contributions		1,142	1,050
Actuarial loss (gain)		5,101	(10,233)
Benefits paid		(3,280)	(4,868)
Fair value of plan assets		39,060	30,800	34,133
Actual return on plan assets		8,087	(998)
Employer contributions		2,000	1,100
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		1,142	1,050
Defined Benefit Plan, Plan Assets, Benefits Paid		2,969	4,485
Balance at December 31		(13,249)	(16,040)
Current liabilities		0	0
Noncurrent liabilities		(13,249)	(16,040)
Balance at December 31		(13,249)	(16,040)
Expected return on plan assets		(2,285)	(2,690)	(2,257)
Amortization of prior service credit		(227)	(1,662)	(1,662)
Amortization of net loss		297	1,338	1,679
Net periodic benefit cost		291	(61)	683
Net gain (loss)		700	6,545	(328)
Prior service cost		0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax		(227)	(1,662)	(1,662)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		297	1,338	1,679
Deferred income taxes (a)		(177)	(2,831)	82
Total recognized in other comprehensive income (loss)		593	3,390	$ (229)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax		0	227
Accumulated loss		(4,110)	(5,108)
Accumulated other comprehensive loss		(4,110)	(4,881)
Deferred income taxes		1,389	1,567
Accumulated other comprehensive loss, net of tax		$ (2,721)	$ (3,314)
Discount rate		3.50%	4.50%
Discount Rates - Retirement and Other Postretirement Plans		4.50%	3.75%	4.25%
Year that the rate reaches the ultimate trend rate		2024	2022
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 2,000
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		3,422
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		3,399
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		3,519
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		3,454
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		3,446
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		16,385
Other Postretirement Benefits Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,043	$ 1,793
Other Postretirement Benefits Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		37,017	29,007
Other Postretirement Benefits Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		39,060	30,800
Other Postretirement Benefits Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,043	1,792
Other Postretirement Benefits Plan [Member] | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Equity securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,043	1,792
Other Postretirement Benefits Plan [Member] | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	1
Other Postretirement Benefits Plan [Member] | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,428	413
Other Postretirement Benefits Plan [Member] | Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Money market funds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,428	414
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		34,589	28,594
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		34,589	28,594
Supplemental Executive Retirement Plan Investments Included in Other Assets[Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at December 31		$ 98,900	87,700
401(k) Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percent of employee matched of eligible compensation		100.00%
Percentage of Each Participants Eligible Compensation		1.00%
Contributions made to the Plan		$ 30,400	$ 28,000	$ 21,100
Profit-sharing contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of Each Participants Eligible Compensation		6.00%