Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income	$ 335,453	$ 272,318	$ 281,203
Income (loss) from discontinued operations, net of tax	287	2,932	(3,783)
Income from continuing operations	335,166	269,386	284,986
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	256,017	220,205	207,486
Deferred income taxes	63,415	59,735	(25,423)
Changes in current assets and liabilities, net of acquisitions:
Receivables	(104,374)	28,234	(108,255)
Inventories	9,331	(46,796)	9,135
Other current assets	(38,283)	(31,814)	(30,588)
Accounts payable	30,079	21,109	26,013
Other current liabilities	51,278	22,285	4,648
Other noncurrent changes	(60,813)	(38,521)	(18,790)
Net cash provided by continuing operations	541,816	503,823	349,212
Net cash provided by (used in) discontinued operations	464	(3,942)	98,799
Net cash provided by operating activities	542,280	499,881	448,011
Investing activities:
Capital expenditures	(576,065)	(568,230)	(341,382)
Acquisitions, net of cash acquired	(55,597)	(167,692)	0
Net proceeds from sale or disposition of property and other	29,812	26,100	126,588
Investments	(2,011)	(2,321)	(1,608)
Net cash used in continuing operations	(603,861)	(712,143)	(216,402)
Net cash provided by discontinued operations	0	1,236	2,234
Net cash used in investing activities	(603,861)	(710,907)	(214,168)
Financing activities:
Issuance of short-term borrowings	169,977	0	0
Repayment of short-term borrowings	(170,000)	0	0
Issuance of long-term debt	599,455	566,829	140,812
Repayment of long-term debt	(468,917)	(174,520)	(217,394)
Proceeds from issuance of common stock	106,848	0	0
Payments of stock issuance costs	0	(10)	0
Dividends paid	(160,256)	(154,573)	(150,727)
Redemption of preferred stock	0	0	(15,600)
Repurchase of common stock	0	(5,020)	(1,684)
Tax withholding on stock-based compensation	(3,015)	(2,330)	(757)
Net cash provided by (used in) financing activities	74,092	230,376	(245,350)
Effect of exchange rate changes on cash and cash equivalents	0	(1)	(1)
Increase (decrease) in cash and cash equivalents	12,511	19,349	(11,508)
Cash and cash equivalents - beginning of year	53,948	34,599	46,107
Cash and cash equivalents - end of year	$ 66,459	$ 53,948	$ 34,599