Subsequent Events (Narrative) (Details) $ / shares in Units, ft² in Thousands, $ in Thousands		2 Months Ended	12 Months Ended
	Jan. 13, 2022 USD ($) $ / shares shares	Feb. 22, 2022 USD ($) ft² storageFacility state	Dec. 31, 2021 USD ($) ft² $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Subsequent Event [Line Items]
Net rentable area (in square feet) | ft²			198,319
Preferred shares per depositary share (in shares) | shares			0.001	0.001	0.001
Shares issued (in USD per share) | $ / shares			$ 25.00	$ 25.00	$ 25.00
Gross proceeds			$ 4,100,000	$ 3,792,500
Subsequent Event | Series S Preferred Stock
Subsequent Event [Line Items]
Stock issued during period (in shares) | shares	10,000,000
Preferred shares per depositary share (in shares) | shares	0.001
Dividend rate percentage	4.10%
Shares issued (in USD per share) | $ / shares	$ 25.00
Gross proceeds	$ 250,000
Issuance costs	$ 7,200
Acquisition of Self-Storage Facilities Other Investments
Subsequent Event [Line Items]
Total cost of acquisition			$ 5,100,000	$ 792,300	$ 439,600
Acquisition of Self-Storage Facilities Other Investments | Subsequent Event
Subsequent Event [Line Items]
Number of self-storage facilities acquired or under contract to be acquired | storageFacility		15
Number of states self-storage facilities acquired or under contracts to be acquired | state		10
Net rentable area (in square feet) | ft²		1,200
Total cost of acquisition		$ 212,400