Fair Value - Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	$ (1,895)	$ (1,203)
Total	(7,626,455)	(7,273,002)
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Total	(937,350)	(1,039,662)
Recurring basis | Significant Unobservable Inputs (Level 3)
Financial Instruments Measured/Discussed at Fair Value
Total	0	0
Total Fair Value | Recurring basis
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(1,895)	(1,203)
Total	(8,563,805)	(8,312,664)
Total Fair Value | Cash Flow Hedges Interest Rate Caps | Recurring basis | Interest Rate Swap
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	3,204	4,308
Interest Rate Caps | Recurring basis | Significant Other Observable Inputs (Level 2) | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	225
Interest Rate Caps | Total Fair Value | Recurring basis | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	225
Interest Rate Caps | Total Fair Value | Fair Value, Nonrecurring | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets		6
Designated as Hedging Instrument | Recurring basis | Significant Other Observable Inputs (Level 2) | Interest Rate Caps
Financial Instruments Measured/Discussed at Fair Value
Derivative assets		6
Unsecured notes | Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(7,624,560)	(7,271,799)
Unsecured notes | Total Fair Value | Recurring basis
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(7,624,560)	(7,271,799)
Secured Notes Payable and Variable Rate Unsecured Term Loan | Recurring basis | Significant Other Observable Inputs (Level 2)
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(940,779)	(1,043,976)
Secured Notes Payable and Variable Rate Unsecured Term Loan | Total Fair Value | Recurring basis
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	$ (940,779)	$ (1,043,976)