CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 1,240,197	$ 1,094,715	$ 3,294,822	$ 2,912,806
Cost of revenues	897,055	790,957	2,469,161	2,160,810
Gross profit	343,142	303,758	825,661	751,996
Selling, administrative and general expenses	81,606	73,612	248,989	239,051
Gain on sale of property, plant & equipment and businesses	2,104	1,488	8,374	4,630
Other operating expense, net	(14,456)	(4,156)	(23,822)	(27,733)
Operating earnings	249,184	227,478	561,224	489,842
Other nonoperating income, net	4,890	3,793	12,708	11,709
Interest expense, net	33,547	82,041	104,566	154,572
Earnings from continuing operations before income taxes	220,527	149,230	469,366	346,979
Income tax expense	40,663	39,080	75,805	81,557
Earnings from continuing operations	179,864	110,150	393,561	265,422
Earnings (loss) on discontinued operations, net of tax	(713)	(1,571)	(1,778)	8,217
Net earnings	179,151	108,579	391,783	273,639
Other comprehensive income, net of tax
Deferred gain on interest rate derivative	0	0	2,496	0
Amortization of prior interest rate derivative loss	53	1,188	171	1,836
Amortization of actuarial loss and prior service cost for benefit plans	1,091	427	3,274	1,281
Other comprehensive income	1,144	1,615	5,941	3,117
Comprehensive income	$ 180,295	$ 110,194	$ 397,724	$ 276,756
Basic earnings (loss) per share
Continuing operations	$ 1.36	$ 0.83	$ 2.97	$ 2.00
Discontinued operations	(0.01)	(0.01)	(0.01)	0.07
Net earnings	1.35	0.82	2.96	2.07
Diluted earnings (loss) per share
Continuing operations	1.34	0.82	2.94	1.97
Discontinued operations	0.00	(0.01)	(0.02)	0.06
Net earnings	$ 1.34	$ 0.81	$ 2.92	$ 2.03
Weighted-average common shares outstanding
Basic	132,392	132,484	132,505	132,510
Assuming dilution	133,894	134,765	134,079	134,853
Depreciation, depletion, accretion and amortization	$ 89,390	$ 79,636	$ 256,463	$ 227,974
Effective tax rate from continuing operations	18.40%	26.20%	16.20%	23.50%