Derivatives (Schedule Of Interest Rate Swaps) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Derivative [Line Items]
Estimated fair value of liability	$ 10,325	$ 10,714	$ 7,775
2006 Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount for all periods	0	0	115,000
Estimated fair value of liability	0	0	1,450
2009 Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount for all periods	0	0	115,000
Estimated fair value of liability	0	0	6,325
2011 Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount for all periods	93,500	93,500	0
Estimated fair value of liability	$ 10,325	$ 10,714	$ 0