SENIOR NOTES PAYABLE AND OTHER DEBT (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt instruments
Total	$ 8,229,589	$ 8,186,315
Capital lease obligations	0	142,412
Unamortized fair value adjustment	92,465	111,623
Unamortized commission fees and discounts	(26,146)	(26,704)
Senior notes payable and other debt	8,295,908	8,413,646
Unsecured revolving credit facilities
Debt instruments
Total	164,734	540,727
6.25% Senior Notes due 2013
Debt instruments
Total	0	269,850
Interest rate (as a percent)		6.25%
Unsecured term loan due 2015
Debt instruments
Total	127,282	130,336
3.125% Senior Notes due 2015
Debt instruments
Total	400,000	400,000
Interest rate (as a percent)	3.125%	3.125%
6% Senior Notes due 2015
Debt instruments
Total	234,420	234,420
Interest rate (as a percent)	6.00%	6.00%
Unsecured term loan due 2017
Debt instruments
Total	375,000	375,000
Unsecured term loan due 2018
Debt instruments
Total	180,000	180,000
2.00% Senior Notes due 2018
Debt instruments
Total	700,000	700,000
Interest rate (as a percent)	2.00%	2.00%
4.00% senior notes due 2019
Debt instruments
Total	600,000	600,000
Interest rate (as a percent)	4.00%	4.00%
2.700% Senior Notes due 2020
Debt instruments
Total	500,000	0
Interest rate (as a percent)	2.70%
4.750% Senior Notes due 2021
Debt instruments
Total	700,000	700,000
Interest rate (as a percent)	4.75%	4.75%
4.25% senior notes due 2022
Debt instruments
Total	600,000	600,000
Interest rate (as a percent)	4.25%	4.25%
3.25% senior notes due 2022
Debt instruments
Total	500,000	500,000
Interest rate (as a percent)	3.25%	3.25%
6.90% Senior Notes due 2037
Debt instruments
Total	52,400	52,400
Interest rate (as a percent)	6.90%	6.90%
6.59% Senior Notes due 2038
Debt instruments
Total	22,973	22,973
Interest rate (as a percent)	6.59%	6.59%
5.45% Senior Notes due 2043
Debt instruments
Total	258,750	0
Interest rate (as a percent)	5.45%
Mortgage loans and other
Debt instruments
Total	2,814,030	2,880,609
Unsecured term loan
Debt instruments
Total	500,000
Mortgage loans
Debt instruments
Total	23,000	23,200
NHP | 6.59% Senior Notes due 2038
Debt instruments
Total	$ 23,000