Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
Interest Expense	$ 47,374		$ 48,078
Notional Amount	711,601			560,945
Fair Value at Significant Other Observable Inputs (Level 2)	(441)			55
Forward Contracts [Member]
Derivative [Line Items]
Notional Amount	150,000	[1]
Type of Derivative	Forward-starting Swap
Strike Rate	2.091%
Effective Date	Jul. 15, 2014
Expiration Date	Jul. 15, 2019
Fair Value at Significant Other Observable Inputs (Level 2)	(681)
Derivative period	5 years
Currently Paying Contracts [Member]
Derivative [Line Items]
Notional Amount	561,601			560,945
Fair Value at Significant Other Observable Inputs (Level 2)	240			55
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge Adjustments [Member]
Derivative [Line Items]
Interest Expense	5,100
Swap 1 [Member] | Currently Paying Contracts [Member]
Derivative [Line Items]
Notional Amount	410,905	[2]		410,905	[2]
Type of Derivative	Swap
Strike Rate	0.717%
Fair Value at Significant Other Observable Inputs (Level 2)	(234)			(76)
Swap 2 [Member] | Currently Paying Contracts [Member]
Derivative [Line Items]
Notional Amount	150,696	[3]		150,040	[3]
Type of Derivative	Swap
Strike Rate	0.925%
Effective Date	Jul. 17, 2012
Expiration Date	Apr. 18, 2017
Fair Value at Significant Other Observable Inputs (Level 2)	$ 474			$ 131
SGD [Member]
Derivative [Line Items]
Exchange rate	0.80			0.79

[1] In January 2014, we entered into a new forward-starting swap agreement with a notional amount of $150.0 million requiring fixed rate interest payments of 2.091% for a five-year period that commences in July 2014.

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

[3] Represents a portion of 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 March 31, 2014 and $0.79 to 1.00 SGD as of December 31, 2013.