CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 854,474	$ 787,328
Cost of revenues	695,140	629,107
Gross profit	159,334	158,221
Selling, administrative and general expenses	78,340	82,383
Gain on sale of property, plant & equipment and businesses	4,164	369
Other operating expense, net	(3,975)	(5,828)
Operating earnings	81,183	70,379
Other nonoperating income, net	5,083	4,045
Interest expense, net	37,774	34,076
Earnings from continuing operations before income taxes	48,492	40,348
Income tax benefit	(4,903)	(3,175)
Earnings from continuing operations	53,395	43,523
Earnings (loss) on discontinued operations, net of tax	(416)	1,398
Net earnings	52,979	44,921
Other comprehensive income, net of tax
Deferred gain on interest rate derivative	2,496	0
Amortization of prior interest rate derivative loss	66	320
Amortization of actuarial loss and prior service cost for benefit plans	1,091	427
Other comprehensive income	3,653	747
Comprehensive income	$ 56,632	$ 45,668
Basic earnings per share
Continuing operations	$ 0.40	$ 0.33
Discontinued operations	0.00	0.01
Net earnings	0.40	0.34
Diluted earnings (loss) per share
Continuing operations	0.40	0.32
Discontinued operations	(0.01)	0.01
Net earnings	$ 0.39	$ 0.33
Weighted-average common shares outstanding
Basic	132,690	132,636
Assuming dilution	134,359	134,968
Cash dividends per share of common stock	$ 0.28	$ 0.25
Depreciation, depletion, accretion and amortization	$ 81,439	$ 71,563
Effective tax rate from continuing operations	(10.10%)	(7.90%)