Mortgage Notes Payable, Revolving Credit Facility, Interest Expense and Amortization of Deferred Debt Costs - Additional Information (Detail) - USD ($)					12 Months Ended
	Jul. 24, 2020	Jul. 14, 2020	Nov. 12, 2019	Jan. 10, 2019	Dec. 31, 2020	Oct. 01, 2021	Oct. 01, 2020	Mar. 03, 2020	Feb. 10, 2020	Dec. 31, 2019	Nov. 21, 2019	Jun. 03, 2019	Jan. 04, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding debt					$ 1,200,000,000
Fixed rate mortgages					827,603,000					$ 821,503,000
Variable rate debt					74,791,000					74,691,000
Principal amount					1,160,251,000					1,100,000,000
Debt outstanding with fixed-rate										938,400,000
Debt outstanding with variable-rate										162,500,000
Remaining loan balance					268,155,000
Unamortized deferred debt costs					9,337,000					9,700,000
Accumulated amortization					8,700,000					7,500,000
Capitalization of debt issuance cost					1,200,000					1,000,000.0				$ 3,200,000
Mortgage Notes Payable
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure					41,000,000.0					41,000,000.0
Fixed rate mortgage notes payable
Debt Instrument [Line Items]
Fixed rate mortgages					980,800,000					938,400,000
Variable rate loans payable
Debt Instrument [Line Items]
Variable rate debt					179,500,000
New Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 400,000,000.0
Extension in line of credit facility period					1 year
Available borrowing capacity					$ 220,300,000
Outstanding line of credit					104,500,000
Letter of credit available borrowing capacity					185,000
New Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 325,000,000.0
Interest rate spread on LIBOR					1.40%
New Facility | Line of Credit | Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Interest rate spread on LIBOR					1.35%
New Facility | Line of Credit | Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Interest rate spread on LIBOR					1.95%
New Facility | Line of Credit | Term Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 75,000,000.0
New Facility | Term Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate spread on LIBOR					1.35%
New Facility | Term Facility | Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Interest rate spread on LIBOR					1.30%
New Facility | Term Facility | Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Interest rate spread on LIBOR					1.90%
Park Van Ness Loan
Debt Instrument [Line Items]
Fixed rate mortgages					$ 66,400,000
Guarantor obligations, maximum exposure					3,300,000		$ 3,300,000
Park Van Ness Loan | Scenario, Forecast
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure						$ 0
Kentlands Square I
Debt Instrument [Line Items]
Remaining loan balance					29,700,000
Waycroft Construction Loan
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure					23,600,000
Remaining loan balance					146,100,000
Broadlands Village
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure					3,800,000
Remaining loan balance					30,500,000
Avenel Business Park
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure					6,300,000
Remaining loan balance					25,200,000
Countryside
Debt Instrument [Line Items]
Remaining loan balance													$ 12,700,000
Olde Forte Village | Four Point Six Five Maturing January Twenty Thirty Four
Debt Instrument [Line Items]
Loan amount				$ 22,100,000
Loan required periodic principal and interest payment				$ 124,700
Loan term				15 years
Loan fixed interest rate				4.65%
Amortization schedule				25 years
Balloon payment to be paid				$ 12,100,000
Briggs Chancy MarketPlace
Debt Instrument [Line Items]
Remaining loan balance												$ 12,400,000
Shops at Monocacy | Four Point Six Five Maturing January Twenty Thirty Four
Debt Instrument [Line Items]
Loan amount			$ 28,500,000
Loan required periodic principal and interest payment			$ 152,600
Loan term			15 years
Loan fixed interest rate			4.14%
Amortization schedule			25 years
Shops at Monocacy | 4.69% fixed rate loan maturing in 2034
Debt Instrument [Line Items]
Balloon payment to be paid			$ 15,100,000
Thruway
Debt Instrument [Line Items]
Remaining loan balance											$ 35,600,000
Ashbrook Marketplace
Debt Instrument [Line Items]
Remaining loan balance					21,900,000
Ashbrook Marketplace | 3.80% Fixed Rate Loan Maturing In 2035
Debt Instrument [Line Items]
Loan amount		$ 22,100,000
Loan required periodic principal and interest payment		$ 114,226
Loan term		15 years
Loan fixed interest rate		3.80%
Amortization schedule		25 years
Balloon payment to be paid		$ 11,500,000
Ashbrook Marketplace | 3.43% Fixed Rate Loan Maturing in 2035
Debt Instrument [Line Items]
Loan amount	$ 30,000,000.0
Loan required periodic principal and interest payment	$ 149,064
Loan term	15 years
Loan fixed interest rate	3.43%
Amortization schedule	25 years
Balloon payment to be paid	$ 15,300,000
Debt Covenant
Debt Instrument [Line Items]
Carrying value of properties collateralized					$ 1,200,000,000					$ 1,100,000,000
Credit agreement leverage ratio					60.00%
Interest coverage ratio required minimum					2.0
Required fixed charge coverage ratio					1.4
Boca Valley Plaza
Debt Instrument [Line Items]
Remaining loan balance									$ 9,200,000
Palm Springs Center
Debt Instrument [Line Items]
Remaining loan balance								$ 7,100,000