SECURED AND UNSECURED DEBT, NET - Credit Facilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Borrowings outstanding at end of period	$ 2,900	$ 3,300
Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	2,000,000
Weighted average daily borrowings during the period ended	55
Maximum daily borrowings during the period ended	$ 20,000
Weighted average interest rate during the period ended	2.60%
Credit facilities
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Borrowings outstanding at end of period	$ 204,590	90,000
Weighted average daily borrowings during the period ended	94,098	253,813
Maximum daily borrowings during the period ended	$ 204,590	$ 314,869
Weighted average interest rate during the period ended	4.30%	4.70%
Interest rate at the end of the period	4.90%	4.00%
Unsecured Revolving credit facility due 2023 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	$ 1,100,000
Term Loan due September 2023 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	350,000
Revolving Credit Facility | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	1,100,000	$ 1,100,000
Unsecured Working Capital Credit Facility due January 2021
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	75,000	75,000
Borrowings outstanding at end of period	16,583	16
Weighted average daily borrowings during the period ended	23,487	26,101
Maximum daily borrowings during the period ended	$ 66,170	$ 64,633
Weighted average interest rate during the period ended	3.10%	2.90%
Interest rate at the end of the period	2.60%	3.30%