Electric utility segment - Regulatory Proceedings (Details)			1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 25, 2019 contract	Apr. 27, 2017 USD ($)	Feb. 28, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / kWh
Electric utility subsidiary [Abstract]
MPIR requested amount		$ 3,600,000	$ 19,800,000
Decoupling order, service reliability performance, historical measurement period (in years)					10 years
Maximum penalty, percent of ROE						0.20%
Service reliability, pending adjusted maximum penalty amount					$ 6,700,000
Dead band percentage above or below the target					3.00%
Call center performance, maximum penalty percentage						0.08%
Call center performance, pending adjusted maximum penalty					$ 1,300,000
Call center performance, maximum penalty amount					$ 2,100,000
Call center, additional penalty accrued						$ 1,300,000
Energy price, renewable projects with storage capacity (in dollars per kilowatt hour) | $ / kWh						0.115
Energy price, renewable energy-only projects (in dollars per kilowatt hour) | $ / kWh						0.095
Expected savings, phase 1, percent						20.00%
Performance incentive mechanism, incentive cap				$ 3,000,000		$ 3,500,000
Expected savings, Phase 2, January 2019						15.00%
Expected savings, Phase 2, February 2019						10.00%
Expected savings, Phase 2, March 2019						5.00%
Performance incentive mechanism penalty				0
Number of contracts which qualified for incentives under Phase 1 | contract	6
Incentives accrued				$ 1,700,000