Derivative Instruments (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Lender accelerated indebtedness repayment threshold amount	$ 75,000,000			$ 75,000,000
Fair value of effective cash flow hedges	(600,000)			(600,000)			(8,700,000)
Ineffective portion of cash flow hedges	0		0	0		0
Interest Expense	47,742,000		41,047,000	143,403,000		116,758,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge Adjustments [Member]
Derivative [Line Items]
Interest Expense				3,300,000
Swap 1 [Member]
Derivative [Line Items]
Notional Amount	69,317,000	[1]		69,317,000	[1]		69,612,000	[1]
Type of Derivative				Swap
Strike Rate	2.98%			2.98%
Effective Date				Apr. 06, 2009
Expiration Date				Nov. 30, 2013
Fair Value at Significant Other Observable Inputs (Level 2)	(275,000)			(275,000)			(1,552,000)
Swap 2 [Member]
Derivative [Line Items]
Notional Amount							13,335,000	[2]
Type of Derivative				Swap
Strike Rate	3.981%			3.981%
Effective Date				May 17, 2006
Expiration Date				Jul. 18, 2013	[3]
Fair Value at Significant Other Observable Inputs (Level 2)							(275,000)
Swap 3 [Member]
Derivative [Line Items]
Notional Amount							9,649,000	[2]
Type of Derivative				Swap
Strike Rate	4.07%			4.07%
Effective Date				Jun. 23, 2006
Expiration Date				Jul. 18, 2013	[3]
Fair Value at Significant Other Observable Inputs (Level 2)							(203,000)
Swap 4 [Member]
Derivative [Line Items]
Notional Amount	8,599,000	[2]		8,599,000	[2]		8,492,000	[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)	(15,000)			(15,000)			(255,000)
Swap 5 [Member]
Derivative [Line Items]
Notional Amount							39,579,000	[2]
Type of Derivative				Swap
Strike Rate	2.703%			2.703%
Effective Date				Dec. 03, 2009
Expiration Date				Sep. 04, 2014	[4]
Fair Value at Significant Other Observable Inputs (Level 2)							(1,617,000)
Swap 6 [Member]
Derivative [Line Items]
Notional Amount	410,905,000	[5]		410,905,000	[5]		410,905,000	[5]
Type of Derivative				Swap
Strike Rate	0.717%			0.717%
Fair Value at Significant Other Observable Inputs (Level 2)	(447,000)			(447,000)			(3,642,000)
Swap 7 [Member]
Derivative [Line Items]
Notional Amount	150,900,000	[6]		150,900,000	[6]		155,099,000	[6]
Type of Derivative				Swap
Strike Rate	0.925%			0.925%
Effective Date				Jul. 17, 2012
Expiration Date				Apr. 18, 2017
Fair Value at Significant Other Observable Inputs (Level 2)	185,000			185,000			(1,131,000)
Cap 1 [Member]
Derivative [Line Items]
Notional Amount	639,721,000			639,721,000			706,671,000
Fair Value at Significant Other Observable Inputs (Level 2)	$ (552,000)			$ (552,000)			$ (8,675,000)
GBP [Member]
Derivative [Line Items]
Exchange rate	1.62			1.62			1.63
EUR [Member]
Derivative [Line Items]
Exchange rate	1.35			1.35			1.32
SGD [Member]
Derivative [Line Items]
Exchange rate	0.80			0.80			0.82

[1] Translation to U.S. dollars is based on exchange rate of $1.62 to £1.00 as of September 30, 2013 and $1.63 to £1.00 as of December 31, 2012.

[2] Translation to U.S. dollars is based on exchange rate of $1.35 to €1.00 as of September 30, 2013 and $1.32 to €1.00 as of December 31, 2012.

[3] The swap agreements were terminated as the mortgage loans were paid in full in July 2013.

[4] The swap agreement was terminated as the mortgage loan was paid in full in June 2013.

[5] Represents the U.S. dollar tranche of the unsecured term loan.

[6] Represents the Singapore dollar tranche of the unsecured term loan. Translation to U.S. dollars is based on exchange rate of $0.80 to 1.00 SGD as of September 30, 2013 and $0.82 to 1.00 SGD as of December 31, 2012.