Subsequent Events (Detail) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 19, 2020 $ / shares	Sep. 30, 2020 USD ($) ft² building $ / shares	Sep. 30, 2019 $ / shares	Sep. 30, 2020 USD ($) ft² building $ / shares	Sep. 30, 2019 $ / shares	Dec. 31, 2019	Oct. 14, 2020 USD ($) ft² building
Subsequent Event [Line Items]
Acquisition Purchase Price | $		$ 352,558		$ 352,558
Number of Buildings | building		40		40
Rentable Square Feet | ft²		1,583,121		1,583,121
Dividends declared per common share (in dollars per share)		$ 0.215	$ 0.185	$ 0.645	$ 0.555
5.875% Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)		0.367188	0.367188	$ 1.101564	1.101564
Preferred Stock, Dividend Rate, Percentage				5.875%		5.875%
5.875% Series B Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)		0.367188	$ 0.367188	$ 1.101564	$ 1.101564
Preferred Stock, Dividend Rate, Percentage				5.875%		5.875%
5.625% Series C Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)		$ 0.351563		$ 1.054689
Preferred Stock, Dividend Rate, Percentage			5.625%	5.625%	5.625%	5.625%
4.43937% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage					4.43937%
4.43937% Cumulative Redeemable Convertible Preferred Units | 4.43937% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage				4.43937%
4.00% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage				4.00%
4.00% Cumulative Redeemable Convertible Preferred Units | 4.00% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage				4.00%
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)	$ 0.215
Dividends Payable, Date of Record	Dec. 31, 2020
Dividends Payable, Date to be Paid	Jan. 15, 2021
Subsequent Event | OP Units
Subsequent Event [Line Items]
Distributions declared (in dollars per share)	$ 0.215
Dividends Payable, Date of Record	Dec. 31, 2020
Distribution Made to Limited Partner, Distribution Date	Jan. 15, 2021
Subsequent Event | 5.875% Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)	$ 0.367188
Dividends Payable, Date of Record	Dec. 15, 2020
Dividends Payable, Date to be Paid	Dec. 31, 2020
Subsequent Event | 5.875% Series B Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)	$ 0.367188
Dividends Payable, Date of Record	Dec. 15, 2020
Dividends Payable, Date to be Paid	Dec. 31, 2020
Subsequent Event | 5.625% Series C Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends per share, declared (in dollars per share)	$ 0.351563
Dividends Payable, Date of Record	Dec. 15, 2020
Dividends Payable, Date to be Paid	Dec. 31, 2020
Subsequent Event | 4.43937% Cumulative Redeemable Convertible Preferred Units | 4.43937% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Distributions declared (in dollars per share)	$ 0.505085
Dividends Payable, Date of Record	Dec. 15, 2020
Distribution Made to Limited Partner, Distribution Date	Dec. 31, 2020
Subsequent Event | 4.00% Cumulative Redeemable Convertible Preferred Units | 4.00% Cumulative Redeemable Convertible Preferred Units
Subsequent Event [Line Items]
Distributions declared (in dollars per share)	$ 0.45
Dividends Payable, Date of Record	Dec. 15, 2020
Distribution Made to Limited Partner, Distribution Date	Dec. 31, 2020
12772-12746 San Fernando Road | Subsequent Event
Subsequent Event [Line Items]
Acquisition Purchase Price | $							$ 22,100
Number of Buildings | building							2
Rentable Square Feet | ft²							140,837