Segment and geographic information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) segment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment and geographic information
Number of reportable segments | segment	4
Project revenues	$ 98.4	$ 106.4
Segment assets	1,441.5	1,660.0	$ 1,456.8
Project Adjusted EBITDA	63.8	62.5
Change in fair value of derivative instruments	1.2	1.2
Depreciation and amortization	34.9	29.9
Interest, net	2.4	2.5
Other project expense		0.2
Project income	25.3	28.7
Administration	6.4	6.1
Interest expense, net	17.3	16.6
Foreign exchange loss	2.5	19.8
Other income, net		(2.5)
Loss from operations before income taxes	(0.9)	(11.3)
Income tax expense (benefit)	(0.3)	1.6
Net income (loss) from continuing operations	(0.6)	(12.9)
East U.S.
Segment and geographic information
Project revenues	36.1	39.4
Segment assets	628.3	802.5
Project Adjusted EBITDA	27.2	30.3
Change in fair value of derivative instruments	0.2	0.7
Depreciation and amortization	11.5	11.0
Interest, net	2.6	2.5
Project income	12.9	16.1
Loss from operations before income taxes	12.9	16.1
Net income (loss) from continuing operations	12.9	16.1
West U.S.
Segment and geographic information
Project revenues	23.4	19.1
Segment assets	304.9	340.4
Project Adjusted EBITDA	9.1	7.5
Depreciation and amortization	10.0	9.9
Interest, net	(0.2)
Project income	(0.7)	(2.4)
Loss from operations before income taxes	(0.7)	(2.4)
Net income (loss) from continuing operations	(0.7)	(2.4)
Canada
Segment and geographic information
Project revenues	38.7	47.7
Segment assets	292.9	439.4
Project Adjusted EBITDA	27.5	24.8
Change in fair value of derivative instruments	3.3	(0.4)
Depreciation and amortization	13.3	8.8
Project income	10.9	16.4
Loss from operations before income taxes	10.9	16.4
Net income (loss) from continuing operations	10.9	16.4
Un-Allocated Corporate
Segment and geographic information
Project revenues	0.2	0.2
Segment assets	215.4	77.7
Project Adjusted EBITDA	0.0	(0.1)
Change in fair value of derivative instruments	(2.3)	0.9
Depreciation and amortization	0.1	0.2
Other project expense		0.2
Project income	2.2	(1.4)
Administration	6.4	6.1
Interest expense, net	17.3	16.6
Foreign exchange loss	2.5	19.8
Other income, net		(2.5)
Loss from operations before income taxes	(24.0)	(41.4)
Income tax expense (benefit)	(0.3)	1.6
Net income (loss) from continuing operations	$ (23.7)	$ (43.0)