SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Revenues:
Total revenues	$ 848,404	$ 811,920	$ 1,700,693	$ 1,617,518
Net real estate property:
Total net real estate property	19,213,750		19,213,750		$ 19,625,220
United States
Revenues:
Total revenues	797,394	761,428	1,601,595	1,517,459
Net real estate property:
Total net real estate property	17,848,183		17,848,183		18,271,829
Canada
Revenues:
Total revenues	44,045	44,736	85,174	88,786
Net real estate property:
Total net real estate property	1,088,065		1,088,065		1,039,561
United Kingdom
Revenues:
Total revenues	6,965	$ 5,756	13,924	$ 11,273
Net real estate property:
Total net real estate property	$ 277,502		$ 277,502		$ 313,830