Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Operating activities:
Net income		$ 414,707		$ 367,489		$ 378,131
Less: income (loss) from discontinued operations, net of tax		(65,718)		116,721		135,609
Income from continuing operations		480,425		250,768		242,522
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		213,598		210,028		198,240
Deferred income taxes		(4,414)		21,248		27,393
Provision for credit losses		13,624		5,595		1,037
Amortization of debt issuance costs		1,207		978		930
Employee stock-based compensation costs		6,309		8,982		12,857
Pension and postretirement benefit plan net periodic benefit credit		(5,380)		(7,323)		(5,990)
Unrealized losses (gains) on investments		(7,493)		10,207		(6,096)
Gains on sales of assets		(8,521)		(6,631)		(6,418)
Gain on tax-free exchange of the retained shares in Knife River		(186,556)		0		0
Changes in current assets and liabilities, net of acquisitions:
Receivables		110,434		(330,809)		(75,380)
Inventories		(27,594)		(15,555)		138
Other current assets		(52,882)		(9,404)		(67,389)
Accounts payable		(76,679)		172,664		25,511
Other current liabilities		66,997		7,569		3,462
Pension and postretirement benefit plan contributions		(7,643)		(82)		(83)
Other noncurrent changes		(22,675)		(10,582)		(51,787)
Net cash provided by continuing operations		492,757		307,653		298,947
Net cash (used in) provided by discontinued operations		(160,130)		202,411		196,830
Net cash provided by operating activities		332,627		510,064		495,777
Investing activities:
Capital expenditures		(519,726)		(478,425)		(485,197)
Acquisitions, net of cash acquired		0		0		(2,500)
Net proceeds from sale or disposition of property		16,474		11,340		14,585
Cost of removal, net of salvage value		1,170		(11,780)		(11,363)
Investments		16,302		(4,138)		(3,136)
Net cash used in continuing operations		(485,780)		(483,003)		(487,611)
Net cash used in discontinued operations		(55,011)		(155,878)		(398,267)
Net cash used in investing activities of continuing operations		(540,791)		(638,881)		(885,878)
Financing activities:
Issuance of short-term borrowings		810,000		38,500		50,000
Repayment of short-term borrowings		(460,901)		0		(100,000)
Issuance of long-term debt		726,700		373,046		272,043
Repayment of long-term debt		(792,998)		(65,764)		(24,758)
Debt issuance costs		(2,521)		(1,129)		(918)
Proceeds from issuance of common stock		0		(150)		88,767
Dividends paid		(161,316)		(176,915)		(171,354)
Repurchase of common stock		(4,811)		(7,399)		(6,701)
Tax withholding on stock-based compensation		(3,040)		(4,904)		(4,126)
Net cash provided by continuing operations		111,113		155,285		102,953
Net cash provided by (used in) discontinued operations		93,509		(112)		281,762
Net cash provided by financing activities		204,622		155,173		384,715
Increase (decrease) in cash, cash equivalents and restricted cash		(3,542)		26,356		(5,386)
Cash, cash equivalents and restricted cash - beginning of year		80,517	[1]	54,161	[1]	59,547
Cash, cash equivalents and restricted cash - end of year	[1]	$ 76,975		$ 80,517		$ 54,161

[1] *Includes cash of discontinued operations of $10.1 million and $10.4 million for the years ended December 31, 2022 and 2021, respectively.