Derivative Activities (Narrative) (Details) (USD $)			12 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2012 December 2012 Transferred Properties [Member]	Dec. 28, 2012 December 2012 Transferred Properties [Member]	Jul. 31, 2012 Interest Rate Contract [Member]	Dec. 31, 2013 Interest Rate Swap [Member]
Derivative [Line Items]
Purchase price adjustment				$ 5,300,000	$ 5,270,000
Deferred premiums associated with natural gas derivative instruments	5,000,000	4,900,000
Notional amount of interest rate swap							410,000,000
Realized loss on early termination of derivative contract						15,000,000
Maximum loss on credit risk derivative contract			$ 1,100,000