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