Derivative Instruments (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 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	9,400,000			9,400,000			5,500,000
Ineffective portion of cash flow hedges	0		0	0		0
Reclassified as increase to interest expense				6,300,000
Notional Amount	703,920,000			703,920,000			246,973,000
Fair Value at Significant Other Observable Inputs (Level 2)	(9,358,000)			(9,358,000)			(5,484,000)
Termination date				January 2012
GBP [Member]
Derivative [Line Items]
Exchange rate	1.62			1.62			1.55
EUR [Member]
Derivative [Line Items]
Exchange rate	1.29			1.29			1.30
SGD [Member]
Derivative [Line Items]
Exchange rate	0.81			0.81
Swap 1 [Member]
Derivative [Line Items]
Notional Amount	69,235,000	[1]		69,235,000	[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)	(1,970,000)			(1,970,000)			(2,363,000)
Swap 2 [Member]
Derivative [Line Items]
Notional Amount	13,053,000	[2]		13,053,000	[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)	(387,000)			(387,000)			(583,000)
Swap 3 [Member]
Derivative [Line Items]
Notional Amount	9,444,000	[2]		9,444,000	[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)	(287,000)			(287,000)			(435,000)
Swap 4 [Member]
Derivative [Line Items]
Notional Amount	8,312,000	[2]		8,312,000	[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)	(324,000)			(324,000)			(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	38,580,000	[2]		38,580,000	[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)	(1,773,000)			(1,773,000)			(1,592,000)
Swap 8 [Member]
Derivative [Line Items]
Notional Amount	410,905,000	[4]		410,905,000	[4]
Type of Derivative				Swap
Strike Rate	0.717			0.717
Effective Date Description				Various
Expiration Date Description				Various
Fair Value at Significant Other Observable Inputs (Level 2)	(4,063,000)			(4,063,000)
Swap 9 [Member]
Derivative [Line Items]
Notional Amount	154,391,000	[5]		154,391,000	[5]
Type of Derivative				Swap
Strike Rate	0.925			0.925
Effective Date				Jul. 06, 2012
Expiration Date				Apr. 18, 2017	[6]
Fair Value at Significant Other Observable Inputs (Level 2)	(554,000)			(554,000)
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	[6]
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	[7]
Termination date				May 9, 2012
Date paid in full				May 04, 2012

[1] Translation to U.S. dollars is based on exchange rate of $1.62 to £1.00 as of September 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 $1.29 to €1.00 as of September 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 tranche of the unsecured term loan.

[5] Represents the Singapore Dollar tranche of the unsecured term loan. Translation to U.S. dollars is based on exchange rate of $0.81 to 1.00 SGD as of September 30, 2012.

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

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