Derivative Financial Instruments (Details 4) (Derivatives in Cash Flow Hedging Relationship, USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Gains and losses from derivatives
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives	$ 2,049,000	$ (42,000)	$ 3,522,000	$ 689,000
Interest Rate collar
Gains and losses from derivatives
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives	611,000	545,000	1,226,000	860,000
Reclassification of gain (loss) from other comprehensive income to earnings
Amount of gain (loss) reclassified from other comprehensive income into earnings - effective portion	700,000	600,000	1,300,000	1,200,000
Interest rate swap
Gains and losses from derivatives
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives	1,376,000	(383,000)	2,239,000	56,000
Interest rate cap
Gains and losses from derivatives
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives	62,000	(204,000)	57,000	(227,000)
Reclassification of gain (loss) from other comprehensive income to earnings
Amount of gain (loss) reclassified from other comprehensive income into earnings - effective portion	$ 0	$ 0	$ 0	$ 0