CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 1,030,763	$ 956,825	$ 1,818,091	$ 1,711,552
Cost of revenues	738,988	664,641	1,366,337	1,254,649
Gross profit	291,775	292,184	451,754	456,903
Selling, administrative and general expenses	82,793	82,681	164,914	159,149
Gain on sale of property, plant & equipment and businesses	2,773	356	3,142	911
Business interruption claims recovery	0	10,962	0	10,962
Impairment of long-lived assets	0	(860)	0	(10,506)
Other operating expense, net	(17,768)	(6,175)	(23,595)	(20,414)
Operating earnings	193,987	213,786	266,387	278,707
Other nonoperating income (expense), net	1,869	29	3,893	(666)
Interest expense, net	38,455	33,333	72,531	67,065
Earnings from continuing operations before income taxes	157,401	180,482	197,749	210,976
Income tax expense	45,652	53,241	42,477	41,772
Earnings from continuing operations	111,749	127,241	155,272	169,204
Earnings (loss) on discontinued operations, net of tax	8,390	(2,532)	9,788	(4,338)
Net earnings	120,139	124,709	165,060	164,866
Other comprehensive income, net of tax
Reclassification adjustment for cash flow hedges	328	301	647	595
Amortization of actuarial loss and prior service cost for benefit plans	427	20	855	40
Other comprehensive income	755	321	1,502	635
Comprehensive income	$ 120,894	$ 125,030	$ 166,562	$ 165,501
Basic earnings (loss) per share
Continuing operations	$ 0.84	$ 0.95	$ 1.17	$ 1.27
Discontinued operations	0.07	(0.02)	0.08	(0.04)
Net earnings	0.91	0.93	1.25	1.23
Diluted earnings (loss) per share
Continuing operations	0.83	0.93	1.15	1.24
Discontinued operations	0.06	(0.01)	0.07	(0.03)
Net earnings	$ 0.89	$ 0.92	$ 1.22	$ 1.21
Weighted-average common shares outstanding
Basic	132,413	133,419	132,524	133,619
Assuming dilution	134,735	136,208	134,925	136,136
Cash dividends per share of common stock	$ 0.25	$ 0.20	$ 0.50	$ 0.40
Depreciation, depletion, accretion and amortization	$ 76,775	$ 71,908	$ 148,339	$ 141,314
Effective tax rate from continuing operations	29.00%	29.50%	21.50%	19.80%