Secured and Unsecured Debt of the Operating Partnership (Details 2) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Capitalized interest and loan fees
Interest expense	$ 21,228	$ 13,088	$ 42,104	$ 25,044
Operating Partnership [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Remaining 2011	72,262		72,262
2012	305,303		305,303
2013	6,373		6,373
2014	262,443		262,443
2015	602,382		602,382
Thereafter	450,028		450,028
Total	1,698,791		1,698,791
Capitalized interest and loan fees
Gross interest expense	23,293	15,897	46,148	30,437
Capitalized interest	(2,065)	(2,809)	(4,044)	(5,393)
Interest expense	21,228	13,088	42,104	25,044
Operating Partnership [Member] \| 4.25% Exchangeable Notes [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Total	$ 172,500		$ 172,500

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

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