Fair Value of Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Interest Rate Swaps 1 [Member]
Interest rate swaps
Notional Amount	$ 250,000
Fixed Interest Rate	5.0185%
Termination Date	May 30, 2012
Fair Value of Liability	1,845
Interest Rate Swaps 2 [Member]
Interest rate swaps
Notional Amount	150,000
Fixed Interest Rate	5.025%
Termination Date	May 30, 2012
Fair Value of Liability	1,108
Interest Rate Swaps 3 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	4.6845%
Termination Date	Sep. 11, 2012
Fair Value of Liability	3,750
Interest Rate Swaps 4 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.352%
Termination Date	Oct. 23, 2012
Fair Value of Liability	1,607
Interest Rate Swaps 5 [Member]
Interest rate swaps
Notional Amount	125,000
Fixed Interest Rate	4.3745%
Termination Date	Nov. 23, 2012
Fair Value of Liability	3,140
Interest Rate Swaps 6 [Member]
Interest rate swaps
Notional Amount	75,000
Fixed Interest Rate	4.38%
Termination Date	Nov. 23, 2012
Fair Value of Liability	1,886
Interest Rate Swaps 7 [Member]
Interest rate swaps
Notional Amount	150,000
Fixed Interest Rate	5.02%
Termination Date	Nov. 30, 2012
Fair Value of Liability	4,524
Interest Rate Swaps 8 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.242%
Termination Date	Feb. 28, 2013
Fair Value of Liability	3,170
Interest Rate Swaps 9 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.023%
Termination Date	May 30, 2013
Fair Value of Liability	5,218
Interest Rate Swaps 10 [Member]
Interest rate swaps
Notional Amount	300,000
Fixed Interest Rate	5.242%
Termination Date	Aug. 06, 2013
Fair Value of Liability	18,940
Interest Rate Swaps 11 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.038%
Termination Date	Aug. 30, 2013
Fair Value of Liability	6,320
Interest Rate Swaps 12 [Member]
Interest rate swaps
Notional Amount	50,000
Fixed Interest Rate	3.586%
Termination Date	Oct. 23, 2013
Fair Value of Liability	2,350
Interest Rate Swaps 13 [Member]
Interest rate swaps
Notional Amount	50,000
Fixed Interest Rate	3.524%
Termination Date	Oct. 23, 2013
Fair Value of Liability	2,303
Interest Rate Swaps 14 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.05%
Termination Date	Nov. 30, 2013
Fair Value of Liability	7,377
Interest Rate Swaps 15 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.07%
Termination Date	Dec. 19, 2013
Fair Value of Liability	5,130
Interest Rate Swaps 16 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	10,301
Interest Rate Swaps 17 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	10,302
Interest Rate Swaps 18 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	5.16%
Termination Date	Jul. 25, 2014
Fair Value of Liability	20,287
Interest Rate Swaps 19 [Member]
Interest rate swaps
Notional Amount	75,000
Fixed Interest Rate	5.0405%
Termination Date	Jul. 25, 2014
Fair Value of Liability	7,405
Interest Rate Swaps 20 [Member]
Interest rate swaps
Notional Amount	125,000
Fixed Interest Rate	5.0215%
Termination Date	Jul. 25, 2014
Fair Value of Liability	12,289
Interest Rate Swaps 21 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	2.621%
Termination Date	Jul. 25, 2014
Fair Value of Liability	4,453
Interest Rate Swaps 22 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.11%
Termination Date	Jul. 25, 2014
Fair Value of Liability	5,550
Interest Rate Swaps 23 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.258%
Termination Date	Jul. 25, 2014
Fair Value of Liability	5,881
Interest Rate Swaps 24 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.693%
Termination Date	Oct. 26, 2014
Fair Value of Liability	9,962
Interest Rate Swaps 25 [Member]
Interest rate swaps
Notional Amount	300,000
Fixed Interest Rate	3.447%
Termination Date	Aug. 08, 2016
Fair Value of Liability	27,989
Interest Rate Swaps 26 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.4285%
Termination Date	Aug. 19, 2016
Fair Value of Liability	18,576
Interest Rate Swaps 27 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.401%
Termination Date	Aug. 19, 2016
Fair Value of Liability	9,185
Interest Rate Swaps 28 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.50%
Termination Date	Aug. 30, 2016
Fair Value of Liability	19,200
Interest Rate Swaps 29 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.005%
Termination Date	Nov. 30, 2016
Fair Value of Liability	$ 7,691