FAIR VALUE OF DERIVATIVES AND FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Fair Value
Notes receivable, net	$ 139,047	$ 157,992
Debt instruments - fair value
Redeemable noncontrolling interests in the Operating Partnership and DownREIT Partnership	1,104,276	856,294
Transfers between levels of fair value hierarchy	0
Carrying Amount \| Fair Value, Measurements, Recurring
Fair Value
Notes receivable, net	139,047	157,992
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	139,056	157,994
Debt instruments - fair value
Total liabilities	5,482,007	5,004,978
Redeemable noncontrolling interests in the Operating Partnership and DownREIT Partnership	1,104,276	856,294
Carrying Amount \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	113	167
Carrying Amount \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivative Asset Designated as Hedging Instrument, Fair Value	9	2
Fair Value \| Fair Value, Measurements, Recurring
Fair Value
Notes receivable, net	149,055	170,411
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	149,064	170,413
Debt instruments - fair value
Total liabilities	5,704,755	5,382,320
Redeemable noncontrolling interests in the Operating Partnership and DownREIT Partnership	1,104,276	856,294
Fair Value \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	113	167
Fair Value \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivative Asset Designated as Hedging Instrument, Fair Value	9	2
Fair Value \| Level 2 \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	9	2
Debt instruments - fair value
Total liabilities	113	167
Redeemable noncontrolling interests in the Operating Partnership and DownREIT Partnership	1,104,276	856,294
Fair Value \| Level 2 \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	113	167
Fair Value \| Level 2 \| Interest rate contracts \| Fair Value, Measurements, Recurring
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivative Asset Designated as Hedging Instrument, Fair Value	9	2
Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Fair Value
Notes receivable, net	149,055	170,411
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	149,055	170,411
Debt instruments - fair value
Total liabilities	5,704,642	5,382,153
Unsecured Debt \| Carrying Amount \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	3,921,028	3,922,314
Unsecured Debt \| Fair Value \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	4,095,997	4,283,045
Unsecured Debt \| Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	4,095,997	4,283,045
Unsecured Debt \| Working Capital Credit Facility \| Carrying Amount \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	27,318	28,024
Unsecured Debt \| Working Capital Credit Facility \| Fair Value \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	27,318	28,024
Unsecured Debt \| Working Capital Credit Facility \| Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	27,318	28,024
Unsecured Debt \| Commercial Paper \| Carrying Amount \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	470,000	190,000
Unsecured Debt \| Commercial Paper \| Fair Value \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	470,000	190,000
Unsecured Debt \| Commercial Paper \| Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	470,000	190,000
Fixed Rate Debt \| Secured Debt \| Mortgages Note Payable \| Carrying Amount \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	1,036,548	837,473
Fixed Rate Debt \| Secured Debt \| Mortgages Note Payable \| Fair Value \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	1,084,327	854,084
Fixed Rate Debt \| Secured Debt \| Mortgages Note Payable \| Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	1,084,327	854,084
Variable Rate Debt \| Secured Debt \| Tax-exempt secured notes payable \| Carrying Amount \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	27,000	27,000
Variable Rate Debt \| Secured Debt \| Tax-exempt secured notes payable \| Fair Value \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	27,000	27,000
Variable Rate Debt \| Secured Debt \| Tax-exempt secured notes payable \| Fair Value \| Level 3 \| Fair Value, Measurements, Recurring
Debt instruments - fair value
Fair value	$ 27,000	$ 27,000

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