Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net income	$ 390,205	$ 335,453	$ 272,318
Income (loss) from discontinued operations, net of tax	(322)	287	2,932
Income from continuing operations	390,527	335,166	269,386
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	285,100	256,017	220,205
Deferred income taxes	(1,801)	63,415	59,735
Changes in current assets and liabilities, net of acquisitions:
Receivables	7,796	(104,374)	28,234
Inventories	(7,221)	9,331	(46,796)
Other current assets	31,601	(38,283)	(31,814)
Accounts payable	15,955	30,079	21,109
Other current liabilities	35,591	51,278	22,285
Other noncurrent changes	12,201	(60,813)	(38,521)
Net cash provided by continuing operations	769,749	541,816	503,823
Net cash provided by (used in) discontinued operations	(1,375)	464	(3,942)
Net cash provided by operating activities	768,374	542,280	499,881
Investing activities:
Capital expenditures	(558,007)	(576,065)	(568,230)
Acquisitions, net of cash acquired	(105,979)	(55,597)	(167,692)
Net proceeds from sale or disposition of property and other	35,557	29,812	26,100
Investments	(1,814)	(2,011)	(2,321)
Net cash used in continuing operations	(630,243)	(603,861)	(712,143)
Net cash provided by discontinued operations	0	0	1,236
Net cash used in investing activities	(630,243)	(603,861)	(710,907)
Financing activities:
Issuance of short-term borrowings	75,000	169,977	0
Repayment of short-term borrowings	(25,000)	(170,000)	0
Issuance of long-term debt	116,973	599,455	566,829
Repayment of long-term debt	(148,634)	(468,917)	(174,520)
Proceeds from issuance of common stock	3,385	106,848	0
Payments of stock issuance costs	0	0	(10)
Dividends paid	(166,405)	(160,256)	(154,573)
Repurchase of common stock	0	0	(5,020)
Tax withholding on stock-based compensation	(362)	(3,015)	(2,330)
Net cash provided by (used in) financing activities	(145,043)	74,092	230,376
Effect of exchange rate changes on cash and cash equivalents	0	0	(1)
Increase (decrease) in cash and cash equivalents	(6,912)	12,511	19,349
Cash and cash equivalents - beginning of year	66,459	53,948	34,599
Cash and cash equivalents - end of year	$ 59,547	$ 66,459	$ 53,948