SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Revenues:
Total revenues	$ 895,490	$ 848,404	$ 1,778,933	$ 1,700,693
Net real estate property:
Total net real estate property	20,539,766		20,539,766		$ 20,394,754
United States
Revenues:
Total revenues	844,623	797,394	1,677,443	1,601,595
Net real estate property:
Total net real estate property	19,190,206		19,190,206		19,105,939
Canada
Revenues:
Total revenues	44,412	44,045	89,008	85,174
Net real estate property:
Total net real estate property	1,056,233		1,056,233		1,037,105
United Kingdom
Revenues:
Total revenues	6,455	$ 6,965	12,482	$ 13,924
Net real estate property:
Total net real estate property	$ 293,327		$ 293,327		$ 251,710