Derivatives (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 derivatives	Jun. 30, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of interest rate hedges recognized in other comprehensive income	$ 5,811
Interest rate hedges gain reclassified as and increase and as a (reduction) to interest expense	114	(85)
Interest rate hedges gain (loss) to be reclassified into interest expense over next 12 months	240
Number of interest rate derivatives held	0
Treasury Locks [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of interest rate derivatives terminated		2
Notional amount of interest rate hedges terminated		150,000
Treasury locks designated as cash flow hedges, fair value		5,300
Treasury locks designated as cash flow hedges, other comprehensive income		$ 5,218