Derivatives (Summary of Derivative Income Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			$ (1,662)	$ 1,977
(Gain) loss on derivatives	1,634	759	1,662	(1,977)
Commodity Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Changes in fair value of derivatives that do not qualify for hedge accounting	1,012	433	768	(5,481)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	591	308	906	3,547
Ineffective portion of derivatives qualifying for hedge accounting	$ 31	$ 18	$ (12)	$ (43)