CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Total revenues	$ 3,890,296	$ 3,592,667	$ 3,422,181
Cost of revenues	2,889,735	2,591,850	2,564,648
Gross profit	1,000,561	1,000,817	857,533
Selling, administrative and general expenses	323,918	314,986	286,844
Gain on sale of property, plant & equipment and businesses	17,827	15,431	9,927
Other operating expense, net	(47,362)	(21,680)	(30,838)
Operating earnings	647,108	679,582	549,778
Other nonoperating income (expense), net	5,293	944	(1,678)
Interest income	4,437	807	345
Interest expense	295,522	134,076	220,588
Earnings from continuing operations before income taxes	361,316	547,257	327,857
Income tax expense (benefit)
Current	354	94,254	89,340
Deferred	(232,429)	30,597	5,603
Total income tax expense (benefit)	(232,075)	124,851	94,943
Earnings from continuing operations	593,391	422,406	232,914
Earnings (loss) on discontinued operations, net of tax (Note 2)	7,794	(2,915)	(11,737)
Net earnings	601,185	419,491	221,177
Other comprehensive income (loss), net of tax
Reclassification adjustment for cash flow hedges	1,862	1,194	5,828
Adjustment for funded status of benefit plans	(14,106)	(20,583)	23,832
Amortization of actuarial loss and prior service cost for benefit plans	2,154	82	11,985
Other comprehensive income (loss)	(10,090)	(19,307)	41,645
Comprehensive income	$ 591,095	$ 400,184	$ 262,822
Basic earnings (loss) per share
Continuing operations	$ 4.48	$ 3.17	$ 1.75
Discontinued operations	0.06	(0.02)	(0.09)
Net earnings	4.54	3.15	1.66
Diluted earnings (loss) per share
Continuing operations	4.40	3.11	1.72
Discontinued operations	0.06	(0.02)	(0.08)
Net earnings	$ 4.46	$ 3.09	$ 1.64
Weighted-average common shares outstanding
Basic	132,513	133,205	133,210
Assuming dilution	134,878	135,790	135,093