Derivatives (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 2011 Interest Rate Swap	Dec. 31, 2012 2011 Interest Rate Swap	Mar. 31, 2012 2011 Interest Rate Swap	Mar. 31, 2013 2006 Interest Rate Swap	Mar. 31, 2013 2009 Interest Rate Swap
Derivative [Line Items]
Notional amount of interest rate derivatives			$ 93,500	$ 93,500	$ 93,500
Fixed rate payments, interest rate			5.50%
Variable rate payment rate			1.75%			1.75%	1.75%
Fair value of collateral pledged to secure interest rate contracts	9,656
Incremental interest expense paid to interest rate swap counterparties	$ 813	$ 749