Acquisitions - Armenia Mountain (Details) (Armenia Mountain [Member], Subsequent Event [Member], USD $) In Millions, unless otherwise specified	0 Months Ended
	Apr. 30, 2015	Apr. 30, 2015 MW
Armenia Mountain [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Member's Interest Purchase Agreement, Name of Business to be Acquired	Armenia Mountain
Member's Interest Purchase Agreement, Consideration	$ 108.0
Member's Interest Purchase Agreement, Percent Ownership to be Acquired	100.00%
Generating Capacity (MW)	100.5	100.5