Fair Value of Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2011
Interest Rate Swaps 1 [Member]
Interest rate swaps
Notional Amount	$ 300,000
Fixed Interest Rate	5.114%
Termination Date	Aug. 08, 2011
Fair Value	1,533
Interest Rate Swaps 2 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	4.7185%
Termination Date	Aug. 19, 2011
Fair Value	605
Interest Rate Swaps 3 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	4.704%
Termination Date	Aug. 19, 2011
Fair Value	603
Interest Rate Swaps 4 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	4.625%
Termination Date	Aug. 19, 2011
Fair Value	592
Interest Rate Swaps 5 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	4.93%
Termination Date	Aug. 30, 2011
Fair Value	1,551
Interest Rate Swaps 6 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.092%
Termination Date	Sep. 18, 2011
Fair Value	1,248
Interest Rate Swaps 7 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.023%
Termination Date	Oct. 23, 2011
Fair Value	869
Interest Rate Swaps 8 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	4.4815%
Termination Date	Oct. 26, 2011
Fair Value	2,712
Interest Rate Swaps 9 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	4.084%
Termination Date	Dec. 03, 2011
Fair Value	3,279
Interest Rate Swaps 10 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.847%
Termination Date	Jan. 04, 2012
Fair Value	1,822
Interest Rate Swaps 11 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.851%
Termination Date	Jan. 04, 2012
Fair Value	1,824
Interest Rate Swaps 12 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.856%
Termination Date	Jan. 04, 2012
Fair Value	1,826
Interest Rate Swaps 13 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.726%
Termination Date	Jan. 08, 2012
Fair Value	3,610
Interest Rate Swaps 14 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.5065%
Termination Date	Jan. 16, 2012
Fair Value	3,514
Interest Rate Swaps 15 [Member]
Interest rate swaps
Notional Amount	250,000
Fixed Interest Rate	5.0185%
Termination Date	May 30, 2012
Fair Value	10,654
Interest Rate Swaps 16 [Member]
Interest rate swaps
Notional Amount	150,000
Fixed Interest Rate	5.025%
Termination Date	May 30, 2012
Fair Value	6,401
Interest Rate Swaps 17 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	4.6845%
Termination Date	Sep. 11, 2012
Fair Value	10,208
Interest Rate Swaps 18 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.352%
Termination Date	Oct. 23, 2012
Fair Value	3,798
Interest Rate Swaps 19 [Member]
Interest rate swaps
Notional Amount	125,000
Fixed Interest Rate	4.3745%
Termination Date	Nov. 23, 2012
Fair Value	6,794
Interest Rate Swaps 20 [Member]
Interest rate swaps
Notional Amount	75,000
Fixed Interest Rate	4.38%
Termination Date	Nov. 23, 2012
Fair Value	4,082
Interest Rate Swaps 21 [Member]
Interest rate swaps
Notional Amount	150,000
Fixed Interest Rate	5.02%
Termination Date	Nov. 30, 2012
Fair Value	9,618
Interest Rate Swaps 22 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.42%
Termination Date	Feb. 28, 2013
Fair Value	5,561
Interest Rate Swaps 23 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.023%
Termination Date	May 30, 2013
Fair Value	8,262
Interest Rate Swaps 24 [Member]
Interest rate swaps
Notional Amount	300,000
Fixed Interest Rate	5.242%
Termination Date	Aug. 06, 2013
Fair Value	27,964
Interest Rate Swaps 25 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.038%
Termination Date	Aug. 30, 2013
Fair Value	9,101
Interest Rate Swaps 26 [Member]
Interest rate swaps
Notional Amount	50,000
Fixed Interest Rate	3.586%
Termination Date	Oct. 23, 2013
Fair Value	3,130
Interest Rate Swaps 27 [Member]
Interest rate swaps
Notional Amount	50,000
Fixed Interest Rate	3.524%
Termination Date	Oct. 23, 2013
Fair Value	3,063
Interest Rate Swaps 28 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.05%
Termination Date	Nov. 30, 2013
Fair Value	9,857
Interest Rate Swaps 29 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.07%
Termination Date	Dec. 19, 2013
Fair Value	5,715
Interest Rate Swaps 30 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value	11,994
Interest Rate Swaps 31 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value	11,998
Interest Rate Swaps 32 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	5.16%
Termination Date	Jul. 25, 2014
Fair Value	23,584
Interest Rate Swaps 33 [Member]
Interest rate swaps
Notional Amount	75,000
Fixed Interest Rate	5.0405%
Termination Date	Jul. 25, 2014
Fair Value	8,571
Interest Rate Swaps 34 [Member]
Interest rate swaps
Notional Amount	125,000
Fixed Interest Rate	5.0215%
Termination Date	Jul. 25, 2014
Fair Value	14,218
Interest Rate Swaps 35 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	2.621%
Termination Date	Jul. 25, 2014
Fair Value	4,349
Interest Rate Swaps 36 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.11%
Termination Date	Jul. 25, 2014
Fair Value	5,788
Interest Rate Swaps 37 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.258%
Termination Date	Jul. 25, 2014
Fair Value	6,222
Interest Rate Swaps 38 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	2.693%
Termination Date	Oct. 26, 2014
Fair Value	7,504	[1]
Interest Rate Swaps 39 [Member]
Interest rate swaps
Notional Amount	300,000
Fixed Interest Rate	3.447%
Termination Date	Aug. 08, 2016
Fair Value	18,662	[2]
Interest Rate Swaps 40 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.4285%
Termination Date	Aug. 19, 2016
Fair Value	12,096	[3]
Interest Rate Swaps 41 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.404%
Termination Date	Aug. 19, 2016
Fair Value	6,019	[4]
Interest Rate Swaps 42 [Member]
Interest rate swaps
Notional Amount	200,000
Fixed Interest Rate	3.50%
Termination Date	Aug. 30, 2016
Fair Value	12,529	[5]
Interest Rate Swaps 43 [Member]
Interest rate swaps
Notional Amount	100,000
Fixed Interest Rate	3.005%
Termination Date	Nov. 30, 2016
Fair Value	$ 4,196

[1] This interest rate swap becomes effective October 26, 2011, concurrent with the termination of swap #8.

[2] This interest rate swap becomes effective August 8, 2011, concurrent with the termination of swap #1

[3] This interest rate swap becomes effective August 19, 2011, concurrent with the termination of swap #2 and #4.

[4] This interest rate swap becomes effective August 19, 2011, concurrent with the termination of swap #3.

[5] This interest rate swap becomes effective August 30, 2011, concurrent with the termination of swap #5.