EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Investments Included in Other Assets, Supplemental Executive Retirement Plan		$ 87,700	$ 93,200
Deferred income taxes (a)		(1,425)	(878)	$ 11,128
Total recognized in other comprehensive income (loss)		4,771	(4,175)	(16,693)
Accumulated other comprehensive loss, net of tax		$ (121,785)	$ (105,411)	$ (101,236)
Expected long-term return on plan assets		8.00%	7.75%	7.75%
Compensation increase rate		3.00%	3.10%	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. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our retirement and other postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation		$ 466,994	$ 481,615	$ 428,386
Service cost		7,339	6,896	6,501
Interest cost		17,659	18,645	19,820
Plan participants’ contributions		0	0
Actuarial loss (gain)		(24,345)	41,678
Benefits paid		(15,274)	(13,990)
Fair value of plan assets		290,684	306,008	261,671
Actual return on plan assets		(12,350)	50,827
Employer contributions		12,300	7,500
Plan participants’ contributions		0	0
Benefits paid		(15,274)	(13,990)
Balance at December 31		(176,310)	(175,607)
Current liabilities		(4,514)	(4,544)
Noncurrent liabilities		(171,796)	(171,063)
Balance at December 31		(176,310)	(175,607)
Defined Benefit Plan, Accumulated Benefit Obligation		434,400	456,600
Expected return on plan assets		(23,917)	(21,376)	(20,348)
Amortization of prior service credit		0	0	0
Amortization of net loss		17,060	13,586	10,966
Net periodic benefit cost		18,141	17,751	16,939
Net gain (loss) arising during the period		(16,351)	(16,572)	(33,043)
Amortization of prior service credit		0	0	0
Amortization of net loss		17,060	13,586	10,966
Deferred income taxes (a)		(18,928)	(960)	8,831
Total recognized in other comprehensive income (loss)		(18,219)	(3,946)	$ (13,246)
Prior service credit		0	0
Accumulated loss		(160,212)	(160,921)
Accumulated other comprehensive loss		(160,212)	(160,921)
Deferred income taxes		43,286	62,214
Accumulated other comprehensive loss, net of tax		$ (116,926)	$ (98,707)
Discount rate		4.50%	3.75%
Compensation increase rate		3.65%	3.00%
Discount Rates - Pension and Postretirement Plans		3.75%	4.50%	5.25%
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		$ 17,014
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		18,164
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		19,215
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		20,279
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		21,362
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		122,012
Pension Plan [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 14,500
Pension Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		153	$ 176,645
Pension Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,961	108,282
Pension Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		4,114	284,927
Pension Plan [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		286,570	21,081
Pension Plan [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		290,684	306,008
Pension Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		58	176,347
Pension Plan [Member] | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	19,199
Pension Plan [Member] | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Equity securities | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		58	195,546
Pension Plan [Member] | Equity securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		116,790	0
Pension Plan [Member] | Equity securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		116,848	195,546
Pension Plan [Member] | Real Estate Funds [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Plan [Member] | Real Estate Funds [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Plan [Member] | Real Estate Funds [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Plan [Member] | Real Estate Funds [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Pension Plan [Member] | Real Estate Funds [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		20,569
Pension Plan [Member] | Real Estate Funds [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		20,569
Pension Plan [Member] | Government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	19,481
Pension Plan [Member] | Government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Government obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	19,481
Pension Plan [Member] | Government obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		48,913	0
Pension Plan [Member] | Government obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		48,913	19,481
Pension Plan [Member] | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	62,981
Pension Plan [Member] | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Corporate obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	62,981
Pension Plan [Member] | Corporate obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		69,377	0
Pension Plan [Member] | Corporate obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		69,377	62,981
Pension Plan [Member] | Common/collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,961	6,621
Pension Plan [Member] | Common/collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,961	6,621
Pension Plan [Member] | Common/collective trusts | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		3,961	6,621
Pension Plan [Member] | Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		95	298
Pension Plan [Member] | Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		95	298
Pension Plan [Member] | Cash | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		95	298
Pension Plan [Member] | Other Investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		30,921	21,081
Pension Plan [Member] | Other Investments | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		30,921	21,081
Unfunded Capital Commitments		$ 0	$ 0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumed Health Care Cost Trend Rate		6.50%	7.00%
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		$ 46,840	$ 57,938	$ 54,823
Service cost		845	662	596
Interest cost		2,108	2,261	2,404
Plan participants’ contributions		1,050	901
Actuarial loss (gain)		(10,233)	3,456
Benefits paid		(4,868)	(4,165)
Fair value of plan assets		30,800	34,133	29,550
Actual return on plan assets		(998)	5,385
Employer contributions		1,100	2,000
Plan participants’ contributions		1,050	901
Benefits paid		(4,485)	(3,703)
Balance at December 31		(16,040)	(23,805)
Current liabilities		0	0
Noncurrent liabilities		(16,040)	(23,805)
Balance at December 31		(16,040)	(23,805)
Expected return on plan assets		(2,690)	(2,257)	(2,124)
Amortization of prior service credit		(1,662)	(1,662)	(1,662)
Amortization of net loss		1,338	1,679	1,046
Net periodic benefit cost		(61)	683	260
Net gain (loss) arising during the period		6,545	(328)	(5,128)
Amortization of prior service credit		(1,662)	(1,662)	(1,662)
Amortization of net loss		1,338	1,679	1,046
Deferred income taxes (a)		(2,831)	82	2,297
Total recognized in other comprehensive income (loss)		3,390	(229)	$ (3,447)
Prior service credit		227	1,889
Accumulated loss		(5,108)	(12,991)
Accumulated other comprehensive loss		(4,881)	(11,102)
Deferred income taxes		1,567	4,398
Accumulated other comprehensive loss, net of tax		$ (3,314)	$ (6,704)
Discount rate		4.50%	3.75%
Discount Rates - Pension and Postretirement Plans		3.75%	4.25%	5.00%
Year that the rate reaches the ultimate trend rate		2022	2022
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year					$ 2,000
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		$ 3,114
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		3,237
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		3,230
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		3,346
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		3,315
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		16,178
Other Postretirement Benefits Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,793	$ 1,951
Other Postretirement Benefits Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		29,007	32,182
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		30,800	34,133
Other Postretirement Benefits Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,792	1,951
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		1,792	1,951
Other Postretirement Benefits Plan [Member] | Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1	0
Other Postretirement Benefits Plan [Member] | Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		413	1,515
Other Postretirement Benefits Plan [Member] | Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Cash | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		414	1,515
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		28,594	30,667
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		$ 28,594	30,667
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		6.00%
Contributions made to the Plan		$ 15,100	13,700	$ 11,900
Profit Sharing Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of Each Participants Eligible Compensation		1.00%
Contributions made to the Plan		$ 12,900	$ 7,400	$ 8,200