SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Revenues:
Total revenues	$ 827,606	$ 704,932	$ 2,445,124	$ 2,044,723
Net real estate property:
Total net real estate property	19,771,586		19,771,586		$ 16,754,254
United States
Revenues:
Total revenues	777,320	665,217	2,294,780	1,957,116
Net real estate property:
Total net real estate property	18,358,283		18,358,283		15,315,950
Canada
Revenues:
Total revenues	42,756	35,129	131,542	78,168
Net real estate property:
Total net real estate property	1,087,829		1,087,829		1,269,710
United Kingdom
Revenues:
Total revenues	7,530	$ 4,586	18,802	$ 9,439
Net real estate property:
Total net real estate property	$ 325,474		$ 325,474		$ 168,594