Derivatives (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative [Line Items]
Fair value of interest rate hedges recognized in other comprehensive income	$ 5,633,000
Interest rate hedges gain reclassified as and increase and as a (reduction) to interest expense	60,000	(56,000)
Interest rate hedges gain (loss) to be reclassified into interest expense over next 12 months	256,000
Forward Contracts [Member]
Derivative [Line Items]
Number of interest rate derivatives held	4
Notional amount of interest rate cash flow hedge derivatives	240,000,000
Other Liabilities and Accumulated Other Comprehensive Income [Member] | Forward Contracts [Member]
Derivative [Line Items]
Interest rate cash flow hedge liability, fair value	$ 1,144,000