SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Revenues:
Total revenues	$ 852,289	$ 805,598
Net real estate property:
Total net real estate property	19,508,481		$ 19,625,220
United States
Revenues:
Total revenues	804,201	756,032
Net real estate property:
Total net real estate property	18,117,507		18,271,829
Canada
Revenues:
Total revenues	41,129	44,050
Net real estate property:
Total net real estate property	1,088,335		1,039,561
United Kingdom
Revenues:
Total revenues	6,959	$ 5,516
Net real estate property:
Total net real estate property	$ 302,639		$ 313,830