Investments (Acquisitions) (Details) - Minnesota solar garden development projects $ in Millions	3 Months Ended
	Dec. 31, 2016 project MW	Sep. 30, 2016 USD ($) project MW	Oct. 31, 2016 project
Schedule of Equity Method Investments [Line Items]
Number of development projects		14
Power generating capacity (in megawatts) | MW		94
Forecast
Schedule of Equity Method Investments [Line Items]
Number of available projects	3
Power generating capacity (in megawatts) | MW	21
Subsequent event
Schedule of Equity Method Investments [Line Items]
Expired projects not acquired			6
Maximum
Schedule of Equity Method Investments [Line Items]
Number of available projects		20
Purchase price | $		$ 41.9
Reimbursed project specific interconnection costs | $		$ 8.7