Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities:
Net income	$ 378,131	$ 390,205	$ 335,453
Income (loss) from discontinued operations, net of tax	400	(322)	287
Income from continuing operations	377,731	390,527	335,166
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	299,214	285,100	256,017
Deferred income taxes	60,250	(1,801)	63,415
Provision for credit losses	1,085	10,576	7,864
Amortization of debt issuance costs	1,333	2,162	1,330
Employee stock-based compensation costs	14,709	13,096	7,353
Pension & postretirement benefit plan net periodic benefit cost (credit)	(4,900)	(3,001)	703
Unrealized gains on investments	(7,728)	(14,563)	(11,445)
Gains on sales of assets	(13,056)	(15,350)	(15,479)
Changes in current assets and liabilities, net of acquisitions:
Receivables	(60,024)	(2,780)	(112,238)
Inventories	(42,302)	(7,221)	9,331
Other current assets	(71,964)	31,601	(38,283)
Accounts payable	15,247	15,955	30,079
Other current liabilities	(17,650)	35,591	51,278
Pension & postretirement benefit plan contributions	(476)	(434)	(25,613)
Other noncurrent changes	(55,367)	30,291	(17,662)
Net cash provided by continuing operations	496,102	769,749	541,816
Net cash provided by (used in) discontinued operations	(325)	(1,375)	464
Net cash provided by operating activities	495,777	768,374	542,280
Investing activities:
Capital expenditures	(659,425)	(558,007)	(576,065)
Acquisitions, net of cash acquired	(237,718)	(105,979)	(55,597)
Net proceeds from sale or disposition of property and other	15,238	35,557	29,812
Investments	(3,973)	(1,814)	(2,011)
Net cash used in investing activities	(885,878)	(630,243)	(603,861)
Financing activities:
Issuance of short-term borrowings	50,000	75,000	170,000
Repayment of short-term borrowings	(100,000)	(25,000)	(170,000)
Issuance of long-term debt	554,027	117,450	603,969
Repayment of long-term debt	(24,979)	(148,634)	(468,917)
Debt issuance costs	(918)	(477)	(4,537)
Proceeds from issuance of common stock	88,767	3,385	106,848
Dividends paid	(171,354)	(166,405)	(160,256)
Repurchase of common stock	(6,701)	0	0
Tax withholding on stock-based compensation	(4,127)	(362)	(3,015)
Net cash provided by (used in) financing activities	384,715	(145,043)	74,092
Increase (decrease) in cash and cash equivalents	(5,386)	(6,912)	12,511
Cash and cash equivalents - beginning of year	59,547	66,459	53,948
Cash and cash equivalents - end of year	$ 54,161	$ 59,547	$ 66,459