SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Revenues:
Total revenues	$ 891,322	$ 751,254	$ 1,775,346	$ 1,492,724
Net real estate property:
Total net real estate property	21,365,096		21,365,096		$ 18,985,559
United States
Revenues:
Total revenues	840,830	724,725	1,675,287	1,444,833
Net real estate property:
Total net real estate property	19,858,871		19,858,871		17,547,255
Canada
Revenues:
Total revenues	44,736	21,821	88,786	43,038
Net real estate property:
Total net real estate property	1,163,102		1,163,102		1,269,710
United Kingdom
Revenues:
Total revenues	5,756	$ 4,708	11,273	$ 4,853
Net real estate property:
Total net real estate property	$ 343,123		$ 343,123		$ 168,594