Long-Term Debt - Project-level Debt Narrative (Details) - Term debt - Permanent financing - USD ($) $ in Millions	Feb. 01, 2017	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Amount of long term debt outstanding		$ 352.7	$ 351.6
South Africa
Debt Instrument [Line Items]
Long-term debt, amount bearing fixed interest		$ 13.3	$ 12.6
South Africa | Minimum
Debt Instrument [Line Items]
Stated interest rate		11.40%	11.40%
South Africa | Maximum
Debt Instrument [Line Items]
Stated interest rate		13.00%	13.00%
India
Debt Instrument [Line Items]
Long-term debt, amount bearing fixed interest		$ 16.4	$ 17.3
India | Minimum
Debt Instrument [Line Items]
Stated interest rate		0.00%	0.00%
India | Maximum
Debt Instrument [Line Items]
Stated interest rate		4.80%
India | Matures in December 2026 | Maximum
Debt Instrument [Line Items]
Stated interest rate			4.80%
Witkop and Soutpan
Debt Instrument [Line Items]
Amount of long term debt outstanding		$ 143.5	$ 136.6
Debt default percentage	2.00%
Boshof
Debt Instrument [Line Items]
Amount of long term debt outstanding		173.7	178.5
ESP Urja and Azure
Debt Instrument [Line Items]
Long-term debt, amount bearing fixed interest		$ 16.3	17.3
ESP Urja and Azure | Matures in September 2026
Debt Instrument [Line Items]
Stated interest rate		4.50%
ESP Urja and Azure | Matures in December 2026
Debt Instrument [Line Items]
Stated interest rate		4.80%
Silver Star Pavilion and Fortune 11
Debt Instrument [Line Items]
Amount of long term debt outstanding		$ 0.7	$ 0.7
Stated interest rate		4.00%	4.00%
Alto Cielo
Debt Instrument [Line Items]
Long-term debt, amount bearing variable interest		$ 0.1
Three-month LIBOR and three-month Johannesburg Interbank Agreed Rate | South Africa
Debt Instrument [Line Items]
Long-term debt, amount bearing variable interest		317.2	$ 315.2
Kuala Lumpur Interbank Offered Rate | Corporate Season power plant
Debt Instrument [Line Items]
Amount of long term debt outstanding		$ 5.1	$ 5.1
Stated interest rate		6.10%	6.10%