Indebtedness Secured Debt (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) loans	Dec. 31, 2014 USD ($) loans	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
gross basis of secured properties	$ 1,190,000
Letters of Credit Outstanding, Amount	3,200
Fair value	3,487,842	$ 4,778,176
Repayments of Secured Debt	245,665	112,877	$ 169,188
Loss on debt extinguishment	(85,713)	(283)	$ (9,433)
Fixed Rate Secured Debt [Member]
Debt Instrument [Line Items]
Fair value	$ 789,095	$ 1,065,301
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Minimum	2.40%
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Maximum	3.90%
number of secured loans repaid | loans	17	9
Repayments of Secured Debt	$ 231,200	$ 99,300
Repaid Debt, Weighted Average Interest Rate	5.41%	5.56%
Secured Debt [Member]
Debt Instrument [Line Items]
Loss on debt extinguishment	$ 3,700