v3.20.2
Segment and geographic information - Geographic (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Revenue and Assets          
Project revenues $ 62.3 $ 71.3 $ 135.0 $ 144.3  
Property, Plant and Equipment, net of accumulated depreciation 493.6   493.6   $ 502.1
PPA'S and other intangible assets, net of accumulated amortization 131.3   131.3   144.3
Assets 848.9 1,002.6 848.9 1,002.6 935.6
United States          
Revenue and Assets          
Project revenues 45.0 52.5 93.5 104.6  
Property, Plant and Equipment, net of accumulated depreciation 357.3   357.3   353.9
PPA'S and other intangible assets, net of accumulated amortization 130.2   130.2   142.8
Assets 676.9   676.9   762.3
Canada          
Revenue and Assets          
Project revenues 17.3 $ 18.8 41.5 $ 39.7  
Property, Plant and Equipment, net of accumulated depreciation 136.3   136.3   148.2
PPA'S and other intangible assets, net of accumulated amortization 1.1   1.1   1.5
Assets $ 172.0   $ 172.0   $ 173.3