BENEFIT PLANS (Combined Funded Status of Plans and their Reconciliation with Related Amounts Recognized in Consolidated Financial Statements) (Details) - Pension Benefits [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Benefit Obligation
Projected benefit obligation at beginning of year		$ 1,091,223	$ 1,006,674
Service cost		5,716	6,715	$ 5,343
Interest cost		35,503	36,230	36,505
Plan amendment	[1]	0	10,869
Actuarial (gain) loss		(118,827)	81,969
Benefits paid		(54,679)	(51,234)
Projected benefit obligation at end of year		958,936	1,091,223	1,006,674
Change in Fair Value of Plan Assets
Fair value of assets at beginning of year		840,901	749,515
Actual return on plan assets		(59,083)	122,597
Employer contributions		109,631	20,023	9,576
Benefits paid		(54,679)	(51,234)
Fair value of assets at end of year		836,770	840,901	$ 749,515
Funded status		(122,166)	(250,322)
Amounts Recognized in the Consolidated Balance Sheets
Noncurrent assets		6,488	4,605
Current liabilities		(9,067)	(9,478)
Noncurrent liabilities		(119,587)	(245,449)
Net amount recognized		(122,166)	(250,322)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial loss		240,199	250,581
Prior service cost		7,828	9,167
Total amount recognized		$ 248,027	$ 259,748

[1] Effective January 2017, we amended the Construction Materials Hourly Plan to increase the multiplier for years of service.