SEGMENT INFORMATION - Revenue and Net Real Estate Property (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenues:
Total revenues	$ 936,538	$ 899,928	$ 2,822,547	$ 2,678,861
Net real estate property:
Total net real estate property	20,020,634		20,020,634		$ 20,622,454
United States
Revenues:
Total revenues	881,477	844,370	2,656,487	2,521,813
Net real estate property:
Total net real estate property	18,721,154		18,721,154		19,253,724
Canada
Revenues:
Total revenues	48,080	48,639	144,366	137,647
Net real estate property:
Total net real estate property	1,021,728		1,021,728		1,070,903
United Kingdom
Revenues:
Total revenues	6,981	$ 6,919	21,694	$ 19,401
Net real estate property:
Total net real estate property	$ 277,752		$ 277,752		$ 297,827