SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Revenues:
Total revenues	$ 899,928	$ 867,116	$ 2,678,861	$ 2,567,809
Net real estate property:
Total net real estate property	20,464,873		20,464,873		$ 20,394,754
United States
Revenues:
Total revenues	844,370	815,719	2,521,813	2,417,314
Net real estate property:
Total net real estate property	19,079,529		19,079,529		19,105,939
Canada
Revenues:
Total revenues	48,639	45,021	137,647	130,195
Net real estate property:
Total net real estate property	1,086,929		1,086,929		1,037,105
United Kingdom
Revenues:
Total revenues	6,919	$ 6,376	19,401	$ 20,300
Net real estate property:
Total net real estate property	$ 298,415		$ 298,415		$ 251,710