Receivables and allowance for expected credit losses (Details 2) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses					$ 2,244	$ (1,158)
Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	$ 10,156	$ 9,716	$ 12,714	$ 15,358	9,716	15,358
Provision for credit losses	509	1,735	(841)	(317)
Less write-offs charged against the allowance	1,385	1,627	1,424	2,669
Credit loss recoveries collected	285	332	299	342
Balance	9,565	10,156	10,748	12,714	9,565	10,748
Electric | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	361	269	678	899	269	899
Provision for credit losses	113	565	(110)	538
Less write-offs charged against the allowance	234	597	341	888
Credit loss recoveries collected	108	124	100	129
Balance	348	361	327	678	348	327
Natural gas distribution | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2,123	1,506	2,950	2,571	1,506	2,571
Provision for credit losses	92	1,369	(103)	1,273
Less write-offs charged against the allowance	939	932	787	1,107
Credit loss recoveries collected	177	180	199	213
Balance	1,453	2,123	2,259	2,950	1,453	2,259
Pipeline | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2	2	2	2	2	2
Provision for credit losses	0	0	0	0
Less write-offs charged against the allowance	0	0	0	0
Credit loss recoveries collected	0	0	0	0
Balance	2	2	2	2	2	2
Construction materials and contracting | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	5,126	5,406	4,842	6,164	5,406	6,164
Provision for credit losses	12	(253)	11	(1,049)
Less write-offs charged against the allowance	108	27	232	273
Credit loss recoveries collected	0	0	0	0
Balance	5,030	5,126	4,621	4,842	5,030	4,621
Construction services | Trade Accounts Receivable
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2,544	2,533	4,242	5,722	2,533	5,722
Provision for credit losses	292	54	(639)	(1,079)
Less write-offs charged against the allowance	104	71	64	401
Credit loss recoveries collected	0	28	0	0
Balance	$ 2,732	$ 2,544	$ 3,539	$ 4,242	$ 2,732	$ 3,539