SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenues:
Total revenues	$ 943,705	$ 883,443
Net real estate property:
Total net real estate property	20,336,981		$ 20,622,454
United States
Revenues:
Total revenues	887,745	832,820
Net real estate property:
Total net real estate property	18,993,773		19,253,724
Canada
Revenues:
Total revenues	48,536	44,595
Net real estate property:
Total net real estate property	1,037,687		1,070,903
United Kingdom
Revenues:
Total revenues	7,424	$ 6,028
Net real estate property:
Total net real estate property	$ 305,521		$ 297,827