Regulatory liabilities (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 26,440	$ 16,303
Regulatory liabilities	448,454	428,790
Total regulatory liabilities	474,894	445,093
Net Regulatory Position	$ 19,857	31,449
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Regulatory liabilities due within one year	$ 4,929	0
Conservation programs
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Regulatory liabilities due within one year	$ 4,126	12
Taxes refundable to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	3,937	3,841
Regulatory liabilities	$ 203,222	215,421
Taxes refundable to customers | Minimum
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Taxes refundable to customers | Maximum
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Over plant lives
Refundable Fuel and Electric Costs
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Regulatory liabilities due within one year	$ 3,253	713
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Regulatory liabilities due within one year	$ 955	6,700
Other regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	9,240	5,037
Regulatory liabilities	$ 1,587	9,168
Other regulatory liabilities | Minimum
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 1 year
Other regulatory liabilities | Maximum
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 15 years
Plant removal and decommissioning costs
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Over plant lives
Regulatory liabilities	$ 208,650	168,152
Cost recovery mechanisms
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 19 years
Regulatory liabilities	$ 14,025	2,919
Accumulated deferred investment tax credit
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	Up to 19 years
Regulatory liabilities	$ 13,594	12,696
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory liability, refund period	**
Regulatory liabilities	$ 7,376	$ 20,434