Risk Management and Use of Derivative Financial Instruments (Narratives) (Details) € in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2016 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 EUR (€)
Summary of Derivative Instruments
Derivative, remaining maturity	6 years 6 months
Total credit exposure on derivatives	$ 43,800,000
Derivatives, net liability position	8,400,000		$ 8,200,000
Aggregate termination value for immediate settlement	8,800,000		8,300,000
Senior Unsecured Credit Facility - Revolver	793,770,000		$ 485,021,000
Individual Counterparty
Summary of Derivative Instruments
Total credit exposure on derivatives	25,700,000
Interest expense
Summary of Derivative Instruments
Estimated amount reclassified from OCI to income, derivatives	2,000,000
Other Income
Summary of Derivative Instruments
Estimated amount reclassified from OCI to income, derivatives	9,900,000
Revolving Credit Facility | EUR
Summary of Derivative Instruments
Senior Unsecured Credit Facility - Revolver | €		€ 374.5		€ 361.0
Senior Unsecured Notes
Summary of Derivative Instruments
Principal Amount	1,500,000,000.0
4.6% Senior Notes | Senior Unsecured Notes
Summary of Derivative Instruments
Principal Amount	$ 500,000,000