CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	[1]	$ 4,856,826	$ 4,929,103	$ 4,382,869
Cost of revenues		3,575,345	3,673,202	3,281,924
Gross profit		1,281,481	1,255,901	1,100,945
Selling, administrative and general expenses		359,772	370,548	333,371
Gain on sale of property, plant & equipment and businesses		3,997	23,752	14,944
Other operating expense, net		(29,975)	(31,647)	(34,805)
Operating earnings		895,731	877,458	747,713
Other nonoperating income (expense), net		(17,540)	9,243	13,000
Interest income		1,567	1,155	554
Interest expense		135,960	130,155	137,977
Earnings from continuing operations before income taxes		743,798	757,701	623,290
Income tax expense
Current		93,948	58,941	40,516
Deferred		61,855	76,257	64,933
Total income tax expense		155,803	135,198	105,449
Earnings from continuing operations		587,995	622,503	517,841
Loss on discontinued operations, net of tax		(3,515)	(4,841)	(2,036)
Net earnings		584,480	617,662	515,805
Other comprehensive income (loss), net of tax
Deferred gain (loss) on interest rate derivative		(14,679)	0	2,496
Amortization of prior interest rate derivative loss		1,689	227	226
Adjustment for funded status of benefit plans		6,366	(26,892)	(207)
Amortization of actuarial loss and prior service cost for benefit plans		23,057	1,142	4,365
Other comprehensive income (loss)		16,433	(25,523)	6,880
Comprehensive income		$ 600,913	$ 592,139	$ 522,685
Basic earnings (loss) per share
Continuing operations		$ 4.44	$ 4.71	$ 3.91
Discontinued operations		(0.03)	(0.04)	(0.01)
Net earnings		4.41	4.67	3.90
Diluted earnings (loss) per share
Continuing operations		4.41	4.67	3.87
Discontinued operations		(0.02)	(0.04)	(0.02)
Net earnings		$ 4.39	$ 4.63	$ 3.85
Weighted-average common shares outstanding
Basic		132,578	132,300	132,393
Assuming dilution		133,245	133,385	133,926

[1] ¹ The geographic markets are defined by states as follows: East market — Arkansas, Delaware, Illinois, Kentucky, Maryland, North Carolina, Pennsylvania, Tennessee, Virginia, and Washington D.C. Gulf Coast market — Alabama, Florida, Georgia, Louisiana, Mexico, Mississippi, Oklahoma, South Carolina and Texas West market — Arizona, California and New Mexico