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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 |  |  |  |  |  |

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