Noncontrolling Interests (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) item shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Noncontrolling Interest [Line Items]
Distributions paid	$ 6,672	$ 7,022	$ 7,392
Acquisition of noncontrolling interests	35,000		14,425
Contributions by noncontrolling interests	$ 4,148	1,720	2,484
Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Permanent noncontrolling interest in subsidiaries, number of self-storage facilities | item	18
Permanent noncontrolling interest in subsidiaries, number of self-storage facilities under construction | item	7
Convertible partnership units | shares	231,978
Income allocated to other permanent noncontrolling interest in subsidiaries	$ 5,100	6,200	6,200
Distributions paid	6,672	7,022	7,392
Acquisition of noncontrolling interests	11,087		6,724
Contributions by noncontrolling interests	4,148	$ 1,720	2,484
Paid-In Capital [Member]
Noncontrolling Interest [Line Items]
Acquisition of noncontrolling interests	$ 23,913		$ 7,701