Goodwill rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Balance at beginning of period	$ 714,963	$ 681,358
Goodwill acquired during the year	50,640	33,214
Measurement period adjustments	(217)	391
Balance at end of period	765,386	714,963
Natural gas distribution
Goodwill [Roll Forward]
Balance at beginning of period	345,736	345,736
Goodwill acquired during the year	0	0
Measurement period adjustments	0	0
Balance at end of period	345,736	345,736
Construction materials and contracting
Goodwill [Roll Forward]
Balance at beginning of period	226,003	217,234
Goodwill acquired during the year	50,640	8,778
Measurement period adjustments	(217)	(9)
Balance at end of period	276,426	226,003
Construction services
Goodwill [Roll Forward]
Balance at beginning of period	143,224	118,388
Goodwill acquired during the year	0	24,436
Measurement period adjustments	0	400
Balance at end of period	$ 143,224	$ 143,224