Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income Tax Contingency [Line Items]
Reconciliation to consolidated net income	$ 3,382	$ 4,243	$ 18,586	$ 14,577
Effective Income Tax Rate Reconciliation, Percent	13.70%	11.80%	15.90%	13.10%
Northwestern Energy Group Inc.
Income Tax Contingency [Line Items]
Reconciliation to consolidated net income	$ 3,400	$ 4,200	$ 18,600	$ 14,600