Business segment data (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business segment data [Line Items]
Revenues	$ 6,973,864	$ 5,680,733	$ 5,532,750
Depreciation, depletion and amortization	327,826	299,214	285,100
Operating income (loss)	573,953	534,219	544,925
Interest expense	119,273	93,984	96,519
Income taxes	94,783	88,920	84,590
Income from continuing operations	367,276	377,731	390,527
Discontinued operations, net of tax	213	400	(322)
Net income	367,489	378,131	390,205
Capital expenditures	656,559	935,806	648,279
Total assets	9,660,781	8,910,435	8,053,372
Property, Plant and Equipment, Gross	9,364,038	8,972,849
Less accumulated depreciation, depletion and amortization	3,272,493	3,216,461	3,133,831
Net property, plant and equipment	6,091,545	5,756,388	5,166,939
Additional information [Abstract]
Net noncash acquisitions, capital expenditure-related accounts payable and AFUDC	1,700	38,700	(15,700)
Electric
Business segment data [Line Items]
Revenues	376,579	349,039	331,538
Depreciation, depletion and amortization	67,802	66,750	62,998
Operating income (loss)	79,655	66,335	63,434
Interest expense	28,526	26,712	26,699
Income taxes	(5,420)	(7,626)	(11,636)
Capital expenditures	133,970	82,427	114,676
Total assets	1,856,258	1,810,695	2,123,693
Property, Plant and Equipment, Gross	2,276,613	2,295,646	2,323,403
Natural gas distribution
Business segment data [Line Items]
Revenues	1,273,249	971,364	847,651
Depreciation, depletion and amortization	89,466	86,065	84,580
Operating income (loss)	91,889	89,173	73,082
Interest expense	42,126	37,265	36,798
Income taxes	7,805	8,366	5,746
Capital expenditures	240,064	170,411	193,048
Total assets	3,214,452	2,929,519	2,302,770
Property, Plant and Equipment, Gross	3,208,060	3,015,164	2,868,853
Pipeline
Business segment data [Line Items]
Revenues	96,567	82,858	85,346
Depreciation, depletion and amortization	26,857	20,569	21,669
Operating income (loss)	55,466	48,078	49,436
Interest expense	11,318	7,010	7,622
Income taxes	10,212	9,594	7,650
Capital expenditures	61,923	234,803	62,224
Total assets	961,893	913,945	703,377
Property, Plant and Equipment, Gross	1,108,141	1,051,868	821,697
Construction materials and contracting
Business segment data [Line Items]
Revenues	2,533,713	2,228,306	2,177,585
Depreciation, depletion and amortization	117,798	100,974	89,626
Operating income (loss)	194,295	191,077	214,498
Interest expense	30,121	19,218	20,577
Income taxes	42,601	43,459	47,431
Capital expenditures	181,917	417,524	191,635
Total assets	2,268,970	2,161,653	1,798,493
Property, Plant and Equipment, Gross	2,489,408	2,347,696	2,028,476
Construction services
Business segment data [Line Items]
Revenues	2,693,756	2,049,082	2,090,685
Depreciation, depletion and amortization	21,468	20,270	23,523
Operating income (loss)	164,644	145,754	147,644
Interest expense	6,354	3,540	4,095
Income taxes	40,788	35,426	35,797
Capital expenditures	36,413	29,140	83,651
Total assets	1,126,323	845,262	818,662
Property, Plant and Equipment, Gross	245,111	225,758	220,796
Other
Business segment data [Line Items]
Revenues	0	84	(55)
Depreciation, depletion and amortization	4,435	4,586	2,704
Operating income (loss)	(11,996)	(6,198)	(3,169)
Interest expense	1,465	342	883
Income taxes	(1,203)	(299)	(398)
Capital expenditures	2,272	1,501	3,045
Total assets	232,885	249,361	306,377
Property, Plant and Equipment, Gross	36,705	36,717	37,545
Intersegment Eliminations
Business segment data [Line Items]
Revenues	(84,176)	(77,606)	(76,969)
Interest expense	(637)	(103)	(155)
Total assets	(1,184,512)	(992,084)	(711,216)
Intersegment Eliminations | Electric
Business segment data [Line Items]
Revenues	(494)	(543)	(491)
Intersegment Eliminations | Natural gas distribution
Business segment data [Line Items]
Revenues	(555)	(576)	(534)
Intersegment Eliminations | Pipeline
Business segment data [Line Items]
Revenues	(59,012)	(59,678)	(58,531)
Intersegment Eliminations | Construction materials and contracting
Business segment data [Line Items]
Revenues	(1,016)	(624)	(417)
Intersegment Eliminations | Construction services
Business segment data [Line Items]
Revenues	(5,494)	(2,555)	(5,038)
Intersegment Eliminations | Other
Business segment data [Line Items]
Revenues	(17,605)	(13,630)	(11,958)
Total Intersegment operating revenues
Business segment data [Line Items]
Revenues	84,176	77,606	76,969
Regulated Operation
Business segment data [Line Items]
Revenues	1,735,759	1,390,343	1,249,146
Income from continuing operations	137,605	143,085	135,103
Regulated Operation | Electric
Business segment data [Line Items]
Revenues	376,579	349,039	331,538
Income from continuing operations	57,077	51,906	55,601
Regulated Operation | Natural gas distribution
Business segment data [Line Items]
Revenues	1,273,249	971,364	847,651
Income from continuing operations	45,171	51,596	44,049
Regulated Operation | Pipeline
Business segment data [Line Items]
Revenues	85,931	69,940	69,957
Income from continuing operations	35,357	39,583	35,453
Regulated Operation | Intersegment Eliminations
Business segment data [Line Items]
Revenues	59,417	60,108	59,002
Regulated Operation | Intersegment Eliminations | Electric
Business segment data [Line Items]
Revenues	494	543	491
Regulated Operation | Intersegment Eliminations | Natural gas distribution
Business segment data [Line Items]
Revenues	555	576	534
Regulated Operation | Intersegment Eliminations | Pipeline
Business segment data [Line Items]
Revenues	58,368	58,989	57,977
Nonregulated Operation
Business segment data [Line Items]
Revenues	5,238,105	4,290,390	4,283,604
Income from continuing operations	229,671	234,646	255,424
Nonregulated Operation | Pipeline
Business segment data [Line Items]
Revenues	10,636	12,918	15,389
Income from continuing operations	(69)	1,313	1,559
Nonregulated Operation | Construction materials and contracting
Business segment data [Line Items]
Revenues	2,533,713	2,228,306	2,177,585
Income from continuing operations	116,220	129,755	147,325
Nonregulated Operation | Construction services
Business segment data [Line Items]
Revenues	2,693,756	2,049,082	2,090,685
Income from continuing operations	124,781	109,402	109,721
Nonregulated Operation | Other
Business segment data [Line Items]
Revenues	0	84	(55)
Income from continuing operations	(11,261)	(5,824)	(3,181)
Nonregulated Operation | Intersegment Eliminations
Business segment data [Line Items]
Revenues	24,759	17,498	17,967
Nonregulated Operation | Intersegment Eliminations | Pipeline
Business segment data [Line Items]
Revenues	644	689	554
Nonregulated Operation | Intersegment Eliminations | Construction materials and contracting
Business segment data [Line Items]
Revenues	1,016	624	417
Nonregulated Operation | Intersegment Eliminations | Construction services
Business segment data [Line Items]
Revenues	5,494	2,555	5,038
Nonregulated Operation | Intersegment Eliminations | Other
Business segment data [Line Items]
Revenues	$ 17,605	$ 13,630	$ 11,958