SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenues:
Total revenues	$ 942,874	$ 943,705
Net real estate property:
Total net real estate property	20,129,597		$ 20,093,657
United States
Revenues:
Total revenues	888,281	887,745
Net real estate property:
Total net real estate property	18,879,373		18,861,163
Canada
Revenues:
Total revenues	47,597	48,536
Net real estate property:
Total net real estate property	978,703		963,588
United Kingdom
Revenues:
Total revenues	6,996	$ 7,424
Net real estate property:
Total net real estate property	$ 271,521		$ 268,906