Segment and geographic information - Geographic (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue and Assets
Project revenue	$ 272.0	$ 281.6
Property, Plant and Equipment, net of accumulated depreciation	491.8	502.1
PPA'S and other intangible assets, net of accumulated amortization	120.3	144.3
Assets	847.2	935.6
United States
Revenue and Assets
Project revenue	184.9	208.4
Property, Plant and Equipment, net of accumulated depreciation	351.2	353.9
PPA'S and other intangible assets, net of accumulated amortization	119.4	142.8
Assets	666.4	762.3
Canada
Revenue and Assets
Project revenue	87.1	73.2
Property, Plant and Equipment, net of accumulated depreciation	140.6	148.2
PPA'S and other intangible assets, net of accumulated amortization	0.9	1.5
Assets	$ 180.8	$ 173.3