Accounts receivable and allowance for doubtful accounts Receivables and allowance for expected credit losses (Details 2) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	$ 8,497
Current Expected Credit Loss Provision	3,555
Write-offs Charged Against the Allowance	1,265
Credit Loss Recoveries Collected	338
Balance at March 31, 2020	11,125
Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	328
Current Expected Credit Loss Provision	555
Write-offs Charged Against the Allowance	500
Credit Loss Recoveries Collected	109
Balance at March 31, 2020	492
Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	1,056
Current Expected Credit Loss Provision	1,156
Write-offs Charged Against the Allowance	624
Credit Loss Recoveries Collected	229
Balance at March 31, 2020	1,817
Construction materials and contracting
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	5,357
Current Expected Credit Loss Provision	694
Write-offs Charged Against the Allowance	68
Credit Loss Recoveries Collected	0
Balance at March 31, 2020	5,983
Construction services
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	1,756
Current Expected Credit Loss Provision	1,150
Write-offs Charged Against the Allowance	73
Credit Loss Recoveries Collected	0
Balance at March 31, 2020	$ 2,833