CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net earnings	$ 221,177,000	$ 204,923,000	$ 24,382,000
Adjustments to reconcile net earnings to net cash provided by operating activities
Depreciation, depletion, accretion and amortization	274,823,000	279,497,000	307,108,000
Net gain on sale of property, plant & equipment and businesses	(9,927,000)	(244,222,000)	(50,978,000)
Proceeds from sale of future production, net of transaction costs (Note 19)	0	0	153,095,000
Contributions to pension plans	(14,047,000)	(5,488,000)	(4,855,000)
Share-based compensation	18,248,000	23,884,000	22,093,000
Excess tax benefits from share-based compensation	(18,376,000)	(3,464,000)	(161,000)
Deferred tax provision (benefit)	3,069,000	18,378,000	(35,063,000)
Cost of debt purchase	67,075,000	72,949,000	0
(Increase) decrease in assets before initial effects of business acquisitions and dispositions
Accounts and notes receivable	(42,164,000)	(25,118,000)	(42,260,000)
Inventories	(20,925,000)	(5,595,000)	(7,700,000)
Prepaid expenses	(5,288,000)	(6,256,000)	(765,000)
Other assets	34,863,000	(13,930,000)	12,374,000
Increase (decrease) in liabilities before initial effects of business acquisitions and dispositions
Accrued interest and income taxes	26,605,000	(3,840,000)	(10,937,000)
Trade payables and other accruals	26,491,000	4,229,000	15,485,000
Other noncurrent liabilities	(42,702,000)	(42,810,000)	(26,602,000)
Other, net	(15,544,000)	7,199,000	1,283,000
Net cash provided by operating activities	503,378,000	260,336,000	356,499,000
Investing Activities
Purchases of property, plant & equipment	(289,262,000)	(224,852,000)	(275,380,000)
Proceeds from sale of property, plant & equipment	8,218,000	26,028,000	17,576,000
Proceeds from sale of businesses, net of transaction costs	0	721,359,000	51,604,000
Payment for businesses acquired, net of acquired cash	(27,198,000)	(284,237,000)	(89,951,000)
Increase in restricted cash	(1,150,000)	0	0
Other, net	(350,000)	33,000	(39,000)
Net cash provided by (used for) investing activities	(309,742,000)	238,331,000	(296,190,000)
Financing Activities
Proceeds from line of credit	441,000,000	93,000,000	156,000,000
Payments of line of credit	(206,000,000)	(93,000,000)	(156,000,000)
Payments of current maturities and long-term debt	(695,060,000)	(579,829,000)	(150,602,000)
Proceeds from issuance of long-term debt	400,000,000	0	0
Debt and line of credit issuance costs	(7,382,000)	0	0
Purchases of common stock	(21,475,000)	0	0
Proceeds from issuance of common stock	0	30,620,000	3,821,000
Dividends paid	(53,214,000)	(28,884,000)	(5,191,000)
Proceeds from exercise of stock options	72,971,000	23,502,000	9,762,000
Excess tax benefits from share-based compensation	18,376,000	3,464,000	161,000
Other, net	(65,000)	(5,000)	0
Net cash used for financing activities	(50,849,000)	(551,132,000)	(142,049,000)
Net increase (decrease) in cash and cash equivalents	142,787,000	(52,465,000)	(81,740,000)
Cash and cash equivalents at beginning of year	141,273,000	193,738,000	275,478,000
Cash and cash equivalents at end of year	$ 284,060,000	$ 141,273,000	$ 193,738,000