Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities:
Consolidated net earnings	$ 10,040	$ 42,307
Adjustments to reconcile consolidated net earnings to net cash provided by operating activities:
Depreciation, depletion and amortization	76,821	70,376
Stock-based compensation expense	9,760	10,275
(Gain) Loss on divestitures and sales of assets	(951)	73
Deferred income taxes	2,029	2,827
Other items, net	(2,269)	(179)
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable, net	20,951	(21,305)
Inventories, net	(8,873)	(15,375)
Accounts payable	7,925	8,536
Other assets and liabilities, net	(10,421)	(23,670)
Net Cash Provided by Operating Activities	105,012	73,865
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(96,259)	(102,095)
Proceeds from divestitures and sales of assets	2,528	539
Payment of railcar construction advances	(8,430)	(37,011)
Reimbursement of railcar construction advances	8,430	37,011
Investments in life insurance contracts, net	99	181
Net Cash Used for Investing Activities	(93,632)	(101,375)
Cash Flows from Financing Activities:
Borrowings of debt		205,000
Repayments of debt	(13)	(45,012)
Payments on capital lease obligations	(829)	(761)
Debt issuance costs	(3,194)
Contributions by owners of noncontrolling interest	129
Dividends paid	(27,885)	(26,560)
Proceeds from exercise of stock options	2,801	3,917
Shares withheld for employees' income tax obligations	(6,380)	(3,695)
Repurchases of common stock		(99,999)
Net Cash (Used for) Provided by Financing Activities	(35,371)	32,890
Net (Decrease) Increase in Cash and Cash Equivalents	(23,991)	5,380
Cash and Cash Equivalents, beginning of period	1,446,364	50,038
Cash and Cash Equivalents, end of period	$ 1,422,373	$ 55,418