Debt and Financial Instruments - Additional Information (Detail)				1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 01, 2022 USD ($)	Jul. 02, 2021 USD ($)	Mar. 27, 2018 USD ($) Option	Mar. 31, 2020 USD ($) Derivative	Jan. 31, 2020 USD ($) Derivative	Sep. 30, 2022 USD ($)	Sep. 30, 2019 USD ($) Derivative	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Net borrowings on the line of credit								$ 18,200,000	$ 40,600,000
Proceeds from lines of credit								18,200,000	$ 40,600,000
Outstanding borrowings under revolving credit agreement						$ 290,100,000		290,100,000		$ 271,900,000
Letters Of Credit Outstanding Amount						3,100,000		3,100,000		3,200,000
Available borrowing capacity						81,800,000		81,800,000		99,900,000
Compensating Balance Amount						0		0
Interest Rate Swap
Debt Instrument [Line Items]
Derivative interest rate cap, net payment received or accrued from counterparties						3,000		414,000
Derivative interest rate cap, offset due to counterparties						428,000		463,000
Interest Rate Swap | Cash Flow Hedge
Debt Instrument [Line Items]
Number of interest rate cap agreements | Derivative				1	1		1
Derivative instruments, fixed rate				0.565%	1.4975%		1.144%
Notional amount				$ 55,000,000	$ 35,000,000		$ 50,000,000
Expiration date of interest rate				Mar. 25, 2027	Sep. 16, 2024		Sep. 16, 2024
Level 2
Debt Instrument [Line Items]
Mortgage loan fair value						48,300,000		48,300,000		59,400,000
Mortgage debt										$ 57,200,000
Derivative interest rate cap, net payment received or accrued from counterparties								1,800,000
Derivative interest rate cap, payment received or accrued from counterparties								662,000
Derivative interest rate cap, offset due to counterparties								2,500,000
Level 2 | Interest Rate Swap
Debt Instrument [Line Items]
Liability derivatives, fair value						$ 12,500,000		$ 12,500,000
Seven Hundred Shadow Lane And Goldring Medical Office Building Fixed Rate Mortgage Loan | Nonrecourse
Debt Instrument [Line Items]
Repayment of mortgage loan	$ 5,100,000
London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Margin points added to the reference rate			1.25%
Base Rate
Debt Instrument [Line Items]
Margin points added to the reference rate			0.25%
Credit Agreement
Debt Instrument [Line Items]
Outstanding borrowing		$ 350,000,000	$ 375,000,000
Net borrowings on the line of credit		350,000,000	$ 50,000,000
Unsecured revolving amended credit agreement terminated date			Jul. 02, 2025
Proceeds from lines of credit		350,000,000	$ 50,000,000
Increase in borrowing capacity		$ 375,000,000
Number of additional six month extension options | Option			2
Credit Agreement | Swingline/Short-Term Loans
Debt Instrument [Line Items]
Outstanding borrowing			$ 30,000,000
Credit Agreement | Letters of Credit
Debt Instrument [Line Items]
Outstanding borrowing			$ 40,000,000
Revolving A Facility
Debt Instrument [Line Items]
Credit facility, Interest Rate Terms								Borrowings under the Credit Agreement will bear interest annually at a rate equal to, at our option, at either LIBOR (for one, three, or six months) or the Base Rate, plus in either case, a specified margin depending on our ratio of debt to total capital, as determined by the formula set forth in the Credit Agreement. The applicable margin ranges from 1.10% to 1.35% for LIBOR loans and 0.10% to 0.35% for Base Rate loans.
Base rate description								the greatest of (a) the Administrative Agent’s prime rate, (b) the federal funds effective rate plus 1/2 of 1% and (c) one month LIBOR plus 1%.
Revolving A Facility | Minimum
Debt Instrument [Line Items]
Facility fee payable on commitment			0.15%
Revolving A Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Margin points added to the reference rate			1.10%
Margin points added to the base rate			1.00%
Revolving A Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Margin points added to the reference rate			0.10%
Revolving A Facility | Minimum | Federal Funds Effective Rate
Debt Instrument [Line Items]
Margin points added to the base rate			0.50%
Revolving A Facility | Maximum
Debt Instrument [Line Items]
Facility fee payable on commitment			0.35%
Revolving A Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Margin points added to the reference rate			1.35%
Revolving A Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Margin points added to the reference rate			0.35%
Revolving B Facility
Debt Instrument [Line Items]
Facility fee payable on commitment								0.20%
Revolving B Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Margin points added to the reference rate								1.20%
Revolving B Facility | Base Rate
Debt Instrument [Line Items]
Margin points added to the reference rate								0.20%