SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues:
Total revenues	$ 942,304	$ 895,490	$ 1,886,009	$ 1,778,933
Net real estate property:
Total net real estate property	20,135,670		20,135,670		$ 20,622,454
United States
Revenues:
Total revenues	887,265	844,623	1,774,975	1,677,443
Net real estate property:
Total net real estate property	18,837,522		18,837,522		19,253,724
Canada
Revenues:
Total revenues	47,750	44,412	96,321	89,008
Net real estate property:
Total net real estate property	1,013,440		1,013,440		1,070,903
United Kingdom
Revenues:
Total revenues	7,289	$ 6,455	14,713	$ 12,482
Net real estate property:
Total net real estate property	$ 284,708		$ 284,708		$ 297,827