CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 1,094,715	$ 1,008,140	$ 2,912,806	$ 2,719,693
Cost of revenues	789,199	703,931	2,155,536	1,958,581
Gross profit	305,516	304,209	757,270	761,112
Selling, administrative and general expenses	73,350	76,311	238,263	235,460
Gain on sale of property, plant & equipment and businesses	1,488	2,023	4,630	2,934
Business interruption claims recovery	0	690	0	11,652
Impairment of long-lived assets	0	0	0	(10,506)
Other operating expense, net	(4,167)	(3,535)	(27,763)	(23,949)
Operating earnings	229,487	227,076	495,874	505,783
Other nonoperating income, net	1,784	990	5,677	325
Interest expense, net	82,041	33,126	154,572	100,192
Earnings from continuing operations before income taxes	149,230	194,940	346,979	405,916
Income tax expense	39,080	49,803	81,557	91,575
Earnings from continuing operations	110,150	145,137	265,422	314,341
Earnings (loss) on discontinued operations, net of tax	(1,571)	(3,113)	8,217	(7,451)
Net earnings	108,579	142,024	273,639	306,890
Other comprehensive income, net of tax
Reclassification adjustment for cash flow hedges	1,188	307	1,836	902
Amortization of actuarial loss and prior service cost for benefit plans	427	20	1,281	61
Other comprehensive income	1,615	327	3,117	963
Comprehensive income	$ 110,194	$ 142,351	$ 276,756	$ 307,853
Basic earnings (loss) per share
Continuing operations	$ 0.83	$ 1.09	$ 2.00	$ 2.36
Discontinued operations	(0.01)	(0.02)	0.07	(0.06)
Net earnings	0.82	1.07	2.07	2.30
Diluted earnings (loss) per share
Continuing operations	0.82	1.07	1.97	2.31
Discontinued operations	(0.01)	(0.02)	0.06	(0.05)
Net earnings	$ 0.81	$ 1.05	$ 2.03	$ 2.26
Weighted-average common shares outstanding
Basic	132,484	133,019	132,510	133,418
Assuming dilution	134,765	135,823	134,853	135,932
Cash dividends per share of common stock	$ 0.25	$ 0.20	$ 0.75	$ 0.60
Depreciation, depletion, accretion and amortization	$ 79,636	$ 72,049	$ 227,974	$ 213,362
Effective tax rate from continuing operations	26.20%	25.50%	23.50%	22.60%