SECURED AND UNSECURED DEBT, NET - Credit Facilities (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
	Oct. 26, 2018	Sep. 30, 2018	Dec. 31, 2017	Aug. 31, 2018
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Borrowings outstanding at end of period		$ 3,300	$ 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
Fixed Rate Debt | Fannie Mae credit facilities
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Repayments of outstanding borrowing	$ 195,800
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
Unsecured Revolving credit facility due 2020
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility				$ 2,000,000
Unsecured Revolving credit facility due 2020 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility				1,100
Unsecured Term Loan Facility due 2020 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility				$ 350,000
Term note due January 2029 | Unsecured Commercial Bank Credit Facility
Summary of short-term bank borrowings under unsecured commercial bank credit facility
Total revolving credit facility	$ 300,000
Interest rate	4.40%
Debt issued price as a percent of principal (as a percent)	99.998%
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
Weighted average daily borrowings during the period ended			2,274
Maximum daily borrowings during the period ended			$ 120,000
Weighted average interest rate during the period ended			1.60%
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		51,010	21,767
Weighted average daily borrowings during the period ended		29,398	26,993
Maximum daily borrowings during the period ended		$ 64,633	$ 68,207
Weighted average interest rate during the period ended		2.80%	2.00%
Interest rate at the end of the period		3.10%	2.50%