Derivative Instruments (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011
Derivative [Line Items]
Lender accelerated indebtedness repayment threshold amount	$ 75,000,000			$ 75,000,000
Fair value of effective cash flow hedges	6,600,000			6,600,000			5,500,000
Ineffective portion of cash flow hedges	0		0	0		0
Reclassified as increase to interest expense				4,700,000
Notional Amount	341,737,000			341,737,000			246,973,000
Fair Value at Significant Other Observable Inputs (Level 2)	(6,635,000)			(6,635,000)			(5,484,000)
Termination date				January 2012
EUR [Member]
Derivative [Line Items]
Exchange rate	1.27			1.27			1.30
GBP [Member]
Derivative [Line Items]
Exchange rate	1.57			1.57			1.55
Swap 1 [Member]
Derivative [Line Items]
Notional Amount	67,265,000	[1]		67,265,000	[1]		66,563,000	[1]
Type of Derivative				Swap
Strike Rate	$ 2.980			$ 2.980
Effective Date				Apr. 06, 2009
Expiration Date				Nov. 30, 2013
Fair Value at Significant Other Observable Inputs (Level 2)	(2,100,000)			(2,100,000)			(2,363,000)
Swap 2 [Member]
Derivative [Line Items]
Notional Amount	12,910,000	[2]		12,910,000	[2]		13,319,000	[2]
Type of Derivative				Swap
Strike Rate	$ 3.981			$ 3.981
Effective Date				May 17, 2006
Expiration Date				Jul. 18, 2013
Fair Value at Significant Other Observable Inputs (Level 2)	(458,000)			(458,000)			(583,000)
Swap 3 [Member]
Derivative [Line Items]
Notional Amount	9,341,000	[2]		9,341,000	[2]		9,636,000	[2]
Type of Derivative				Swap
Strike Rate	$ 4.070			$ 4.070
Effective Date				Jun. 23, 2006
Expiration Date				Jul. 18, 2013
Fair Value at Significant Other Observable Inputs (Level 2)	(340,000)			(340,000)			(435,000)
Swap 4 [Member]
Derivative [Line Items]
Notional Amount	8,220,000	[2]		8,220,000	[2]		8,480,000	[2]
Type of Derivative				Swap
Strike Rate	$ 3.989			$ 3.989
Effective Date				Jul. 27, 2006
Expiration Date				Oct. 18, 2013
Fair Value at Significant Other Observable Inputs (Level 2)	(360,000)			(360,000)			(432,000)
Swap 5 [Member]
Derivative [Line Items]
Notional Amount							39,483,000	[2]
Type of Derivative				Swap
Strike Rate	$ 3.776			$ 3.776
Effective Date				Dec. 05, 2006
Expiration Date				Jan. 18, 2012	[3]
Fair Value at Significant Other Observable Inputs (Level 2)							(41,000)
Swap 6 [Member]
Derivative [Line Items]
Notional Amount							33,946,000	[2]
Type of Derivative				Swap
Strike Rate	$ 4.000			$ 4.000
Effective Date				Dec. 20, 2006
Expiration Date				Jan. 18, 2012	[3]
Fair Value at Significant Other Observable Inputs (Level 2)							(38,000)
Swap 7 [Member]
Derivative [Line Items]
Notional Amount	38,001,000	[2]		38,001,000	[2]		38,883,000	[2]
Type of Derivative				Swap
Strike Rate	$ 2.703			$ 2.703
Effective Date				Dec. 03, 2009
Expiration Date				Sep. 04, 2014
Fair Value at Significant Other Observable Inputs (Level 2)	(1,695,000)			(1,695,000)			(1,592,000)
Swap 8 [Member]
Derivative [Line Items]
Notional Amount	206,000,000	[4]		206,000,000	[4]
Type of Derivative				Swap
Strike Rate	$ 0.932			$ 0.932
Effective Date				Jun. 18, 2012
Expiration Date				Apr. 18, 2017
Fair Value at Significant Other Observable Inputs (Level 2)	(1,682,000)			(1,682,000)
Cap 1 [Member]
Derivative [Line Items]
Notional Amount							16,163,000
Type of Derivative				Cap
Strike Rate	$ 4.000			$ 4.000
Effective Date				Jun. 24, 2009
Expiration Date				Jun. 25, 2012	[5]
Termination date				April 27, 2012
Date paid in full				Apr. 26, 2012
Cap 2 [Member]
Derivative [Line Items]
Notional Amount							$ 20,500,000
Type of Derivative				Cap
Strike Rate	$ 4.000			$ 4.000
Effective Date				Aug. 04, 2010
Expiration Date				Jun. 15, 2013	[6]
Termination date				May 9, 2012
Date paid in full				May 04, 2012

[1] Translation to U.S. dollars is based on exchange rate of $1.57 to £1.00 as of June 30, 2012 and $1.55 to £1.00 as of December 31, 2011.

[2] Translation to U.S. dollars is based on exchange rate of $1.27 to €1.00 as of June 30, 2012 and $1.30 to €1.00 as of December 31, 2011.

[3] The swap agreements were terminated as the mortgage loans were paid in full at maturity in January 2012.

[4] Represents the U.S. Dollar portion of the unsecured term loan.

[5] This cap agreement was terminated on April 27, 2012 as the mortgage loan was paid in full on April 26, 2012.

[6] This cap agreement was terminated on May 9, 2012 as the loans were paid in full on May 4, 2012.