Disclosures About Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Summary of financial instruments
Senior unsecured notes	$ 7,625,041	$ 6,963,375
Mortgage debt	1,199,633	1,396,485
Other debt	97,845	74,909
Carrying Value
Summary of financial instruments
Loans receivable, net	418,801	366,001
Marketable debt securities	239,801	244,089
Marketable equity securities	26
Term loan	222,118	226,858
Senior unsecured notes	7,625,041	6,963,375
Mortgage debt	1,199,633	1,396,485
Other debt	97,845	74,909
Derivative assets	1,447	2,325
Derivative liabilities	7,580	8,384
Carrying Value | Warrants
Summary of financial instruments
Derivative assets	69	114
Carrying Value | Currency Swap [Member]
Summary of financial instruments
Derivative assets	484
Derivative liabilities	1,337	2,756
Fair Value | Level 1
Summary of financial instruments
Marketable debt securities	272,420	280,850
Marketable equity securities	26
Senior unsecured notes	8,144,262	7,405,817
Fair Value | Level 2
Summary of financial instruments
Loans receivable, net	426,598	373,441
Term loan	222,118	226,858
Mortgage debt	1,234,725	1,421,214
Other debt	97,845	74,909
Derivative assets	1,447	2,325
Derivative liabilities	7,580	8,384
Fair Value | Warrants | Level 3
Summary of financial instruments
Derivative assets	69	114
Fair Value | Currency Swap [Member]
Summary of financial instruments
Derivative assets	484
Fair Value | Currency Swap [Member] | Level 2
Summary of financial instruments
Derivative liabilities	$ 1,337	$ 2,756