SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Revenues:
Total revenues	$ 883,443	$ 852,289
Net real estate property:
Total net real estate property	20,615,729		$ 20,394,754
United States
Revenues:
Total revenues	832,820	804,201
Net real estate property:
Total net real estate property	19,325,618		19,105,939
Canada
Revenues:
Total revenues	44,595	41,129
Net real estate property:
Total net real estate property	1,036,815		1,037,105
United Kingdom
Revenues:
Total revenues	6,028	$ 6,959
Net real estate property:
Total net real estate property	$ 253,296		$ 251,710