SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Revenues:
Total revenues	$ 867,116	$ 827,606	$ 2,567,809	$ 2,445,124
Net real estate property:
Total net real estate property	20,601,402		20,601,402		$ 19,625,220
United States
Revenues:
Total revenues	815,719	777,320	2,417,314	2,294,780
Net real estate property:
Total net real estate property	19,266,865		19,266,865		18,271,829
Canada
Revenues:
Total revenues	45,021	42,756	130,195	131,542
Net real estate property:
Total net real estate property	1,066,924		1,066,924		1,039,561
United Kingdom
Revenues:
Total revenues	6,376	$ 7,530	20,300	$ 18,802
Net real estate property:
Total net real estate property	$ 267,613		$ 267,613		$ 313,830