Regulatory Environment - MERC (Details) - 2018 rates - Minnesota Public Utilities Commission (MPUC) - MERC - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 3.1
Approved rate increase (as a percent)	1.26%
Approved return on equity (as a percent)	9.70%
Approved common equity component average (as a percent)	50.90%
Interim rates refunded to customers		$ 8.2