Accounts receivable and allowance for doubtful accounts Receivables and allowance for expected credit losses (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	$ 11,090	$ 11,125	$ 8,497
Current expected credit loss provision	3,611	1,075	3,555
Less write-offs charged against the allowance	1,307	1,399	1,265
Credit loss recoveries collected	278	289	338
Balance	13,672	11,090	11,125
Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	659	492	328
Current expected credit loss provision	435	303	555
Less write-offs charged against the allowance	269	224	500
Credit loss recoveries collected	75	88	109
Balance	900	659	492
Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	1,531	1,817	1,056
Current expected credit loss provision	811	190	1,156
Less write-offs charged against the allowance	692	677	624
Credit loss recoveries collected	203	201	229
Balance	1,853	1,531	1,817
Pipeline
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	0	0	0
Current expected credit loss provision	2	0	0
Less write-offs charged against the allowance	0	0	0
Credit loss recoveries collected	0	0	0
Balance	2	0	0
Construction materials and contracting
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	5,625	5,983	5,357
Current expected credit loss provision	728	(314)	694
Less write-offs charged against the allowance	229	44	68
Credit loss recoveries collected	0	0	0
Balance	6,124	5,625	5,983
Construction services
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	3,275	2,833	1,756
Current expected credit loss provision	1,635	896	1,150
Less write-offs charged against the allowance	117	454	73
Credit loss recoveries collected	0	0	0
Balance	$ 4,793	$ 3,275	$ 2,833