Acquisitions

9 Months Ended

Sep. 30, 2012

Disclosure Text Block [Abstract]

Acquisitions

2.  Acquisitions

The acquisitions of the Platte Valley assets in February 2011 and the Wattenberg Plant in May 2011 constitute business combinations and were accounted for using the acquisition method.Preliminary fair-value measurements of assets acquired and liabilities assumed were finalized in the first quarter of 2012, and were equal to the amounts included on the Company's Consolidated Balance Sheet as of December 31, 2011.