CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 1,200,151	$ 1,030,763	$ 2,054,625	$ 1,818,091
Cost of revenues	876,967	740,746	1,572,106	1,369,853
Gross profit	323,184	290,017	482,519	448,238
Selling, administrative and general expenses	89,043	83,056	167,383	165,439
Gain on sale of property, plant & equipment and businesses	2,106	2,773	6,270	3,142
Other operating expense, net	(5,994)	(17,768)	(9,969)	(23,595)
Operating earnings	230,253	191,966	311,437	262,346
Other nonoperating income, net	3,339	3,890	8,421	7,934
Interest expense, net	33,244	38,455	71,018	72,531
Earnings from continuing operations before income taxes	200,348	157,401	248,840	197,749
Income tax expense	40,046	45,652	35,143	42,477
Earnings from continuing operations	160,302	111,749	213,697	155,272
Earnings (loss) on discontinued operations, net of tax	(650)	8,390	(1,066)	9,788
Net earnings	159,652	120,139	212,631	165,060
Other comprehensive income, net of tax
Deferred gain on interest rate derivative	0	0	2,496	0
Amortization of prior interest rate derivative loss	52	328	118	647
Amortization of actuarial loss and prior service cost for benefit plans	1,092	427	2,183	855
Other comprehensive income	1,144	755	4,797	1,502
Comprehensive income	$ 160,796	$ 120,894	$ 217,428	$ 166,562
Basic earnings (loss) per share
Continuing operations	$ 1.21	$ 0.84	$ 1.61	$ 1.17
Discontinued operations	0.00	0.07	(0.01)	0.08
Net earnings	1.21	0.91	1.60	1.25
Diluted earnings (loss) per share
Continuing operations	1.20	0.83	1.59	1.15
Discontinued operations	(0.01)	0.06	(0.01)	0.07
Net earnings	$ 1.19	$ 0.89	$ 1.58	$ 1.22
Weighted-average common shares outstanding
Basic	132,437	132,413	132,563	132,524
Assuming dilution	134,051	134,735	134,280	134,925
Cash dividends per share of common stock	$ 0.28	$ 0.25	$ 0.56	$ 0.50
Depreciation, depletion, accretion and amortization	$ 85,633	$ 76,775	$ 167,072	$ 148,339
Effective tax rate from continuing operations	20.00%	29.00%	14.10%	21.50%