Regulatory liabilities (Details 2) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 18,599	$ 16,303	$ 16,491
Regulatory liabilities	433,212	428,790	426,141
Total regulatory liabilities	451,811	445,093	442,632
Net regulatory position	40,791	31,449	69,748
Taxes refundable to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	4,264	3,841	3,867
Regulatory liabilities	$ 205,517	215,421	218,566
Taxes refundable to customers | Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 1 year
Taxes refundable to customers | Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Over plant lives
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 1 year
Regulatory liabilities due within one year	$ 3,763	0	3,205
Cost Recovery Mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	2,674	214	2,797
Regulatory liabilities	$ 12,535	7,727	0
Cost Recovery Mechanisms | Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 1 year
Cost Recovery Mechanisms | Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 20 years
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 1 year
Regulatory liabilities due within one year	$ 873	6,700	0
Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	7,025	5,548	6,622
Regulatory liabilities	$ 6,327	4,360	5,574
Other regulatory liabilities | Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 1 year
Other regulatory liabilities | Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 16 years
Plant removal and decommissioning costs
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Over plant lives
Regulatory liabilities	$ 174,481	168,152	172,683
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	**
Regulatory liabilities	$ 19,687	20,434	16,915
Accumulated Deferred ITC
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of September 30, 2022	Up to 20 years
Regulatory liabilities	$ 14,665	$ 12,696	$ 12,403