Derivative Instruments (Details) $ in Thousands		1 Months Ended	3 Months Ended			9 Months Ended
	Jan. 13, 2015 USD ($)	Jan. 31, 2014	Sep. 30, 2015 USD ($) $ / SGD	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) $ / SGD	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) $ / SGD
Derivative [Line Items]
Notional Amount			$ 469,142			$ 469,142		$ 703,870
Fair Value at Significant Other Observable Inputs (Level 2)			(67)			(67)		$ (2,409)
Interest Expense			$ 48,138		$ 48,169	139,718	$ 144,689
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge adjustments
Derivative [Line Items]
Interest Expense						$ 1,900
Cash Flow Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Term of contract		5 years
Loss on hedge				$ 1,600
Cash settlement	$ 5,700
SGD
Derivative [Line Items]
Exchange rate | $ / SGD			0.70			0.70		0.75
Currently-paying contracts
Derivative [Line Items]
Notional Amount			$ 469,142			$ 469,142		$ 553,870
Fair Value at Significant Other Observable Inputs (Level 2)			(67)			(67)		428
Currently-paying contracts | Swap 1
Derivative [Line Items]
Notional Amount			$ 335,905			$ 335,905		410,905
Type of Derivative						Swap
Strike Rate			0.717%			0.717%
Fair Value at Significant Other Observable Inputs (Level 2)			$ (1,502)			$ (1,502)		(241)
Currently-paying contracts | Swap 2
Derivative [Line Items]
Notional Amount			$ 133,237			$ 133,237		142,965
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)			$ 1,435			$ 1,435		669
Forward-starting contracts
Derivative [Line Items]
Notional Amount			$ 0			$ 0		150,000
Type of Derivative						Forward-starting Swap
Strike Rate			2.091%			2.091%
Effective Date						Jul. 15, 2014
Expiration Date						Jul. 15, 2019
Fair Value at Significant Other Observable Inputs (Level 2)			$ 0			$ 0		$ (2,837)