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Condensed Statements of Cash Flows (Details 3) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items] |  |  |
Operating activities: | $ 768,374 | $ 542,280 | $ 499,881
Capital expenditures | (558,007) | (576,065) | (568,230)
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 investing activities | (630,243) | (603,861) | (710,907)
Issuance of long-term debt | 116,973 | 599,455 | 566,829
Repayment of long-term debt | (148,634) | (468,917) | (174,520)
Payments of stock issuance costs | 0 | 0 | (10)
Proceeds from issuance of common stock | 3,385 | 106,848 | 0
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 used in financing activities | (145,043) | 74,092 | 230,376
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
MDU Resources Group, Inc. [Member] |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |
Operating activities: | 226,642 | 168,520 | 294,379
Capital expenditures | 0 | 0 | (242,692)
Net proceeds from sale or disposition of property and other | 0 | 0 | 5,032
Investments in and advances to subsidiaries | (67,000) | (120,000) | (40,000)
Advances from subsidiaries | 0 | 17,000 | 70,000
Investments | (4) | (236) | (528)
Net cash used in investing activities | (67,004) | (103,236) | (208,188)
Issuance of long-term debt | 0 | 0 | 199,422
Repayment of long-term debt | 0 | 0 | (125,961)
Payments of stock issuance costs | 0 | 0 | (10)
Proceeds from issuance of common stock | 3,385 | 106,848 | 0
Dividends paid | (166,405) | (160,256) | (154,573)
Repurchase of common stock | 0 | 0 | (1,920)
Tax withholding on stock-based compensation | (163) | (1,821) | (1,721)
Net cash used in financing activities | (163,183) | (55,229) | (84,763)
Increase (decrease) in cash and cash equivalents | (3,545) | 10,055 | 1,428
Cash and cash equivalents - beginning of year | 12,326 | 2,271 | 843
Cash and cash equivalents - end of year | $ 8,781 | $ 12,326 | $ 2,271

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