Acquisitions - Armenia Mountain (Details) - Armenia Mountain [Member] $ in Millions		6 Months Ended
	Jul. 01, 2015 USD ($) MW	Jun. 30, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition Related Costs		$ 0.7
Subsequent Event [Member]
Business Acquisition [Line Items]
Date of Acquisition	Jul. 01, 2015
Percentage of Voting Interests Acquired	100.00%
Name of Acquired Entity	Armenia Mountain
Payments to Acquire Businesses	$ 108.0
Initial Accounting Incomplete, Reasons	We are currently in the process of accounting for the acquisition, therefore, certain disclosures, including the allocation of the purchase price, will be included in the Form 10-Q for the period ending September 30, 2015.
Generating Capacity (MW) | MW	100.5