Disclosures About Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Summary of financial instruments
Marketable equity securities		$ 24,829
Senior unsecured notes	6,963,375	6,712,624
Mortgage debt	1,396,485	1,665,210
Other debt	74,909	81,958
Carrying Value
Summary of financial instruments
Loans receivable, net	366,001	276,030
Marketable debt securities	244,089	222,809
Marketable equity securities		24,829
Term loan	226,858	222,694
Senior unsecured notes	6,963,375	6,712,624
Mortgage debt	1,396,485	1,676,544
Other debt	74,909	81,958
Carrying Value | Warrants
Summary of financial instruments
Derivative assets	114	670
Carrying Value | Interest-rate swap contracts
Summary of financial instruments
Derivative assets	2,325	89
Derivative liabilities	8,384	12,699
Carrying Value | Currency swap contracts
Summary of financial instruments
Derivative liabilities	2,756	2,641
Fair Value | Level 1
Summary of financial instruments
Marketable equity securities		24,829
Senior unsecured notes	7,405,817	7,432,012
Fair Value | Level 2
Summary of financial instruments
Loans receivable, net	373,441	279,850
Term loan	226,858	222,694
Mortgage debt	1,421,214	1,771,155
Other debt	74,909	81,958
Fair Value | Level 3
Summary of financial instruments
Marketable debt securities	280,850	234,137
Fair Value | Warrants | Level 3
Summary of financial instruments
Derivative assets	114	670
Fair Value | Interest-rate swap contracts | Level 2
Summary of financial instruments
Derivative assets	2,325	89
Derivative liabilities	8,384	12,699
Fair Value | Currency swap contracts | Level 2
Summary of financial instruments
Derivative liabilities	$ 2,756	$ 2,641