Mortgage Notes Payable, Revolving Credit Facility, Interest Expense and Amortization of Deferred Debt Costs - Summary of Notes Payable (Additional Information) (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) note shopping_center	Dec. 31, 2016	Dec. 31, 2012 USD ($)
Notes Payable [Line Items]
Interest rate	3.90%	4.25%
Fixed rate mortgage notes payable
Notes Payable [Line Items]
Interest rate	5.25%
Fixed rate mortgage notes payable | 6.01% due February 2018
Notes Payable [Line Items]
Interest rate	6.01%
Fixed rate mortgage notes payable | 6.01% due February 2018 | Washington Square
Notes Payable [Line Items]
Principal and interest payments	$ 264,000
Balloon payment to be paid	$ 28,000,000
Amortization period	27 years 6 months
Loan amount	$ 60,000,000.0
Fixed rate mortgage notes payable | 5.88% due January 2019
Notes Payable [Line Items]
Interest rate	5.88%
Fixed rate mortgage notes payable | 5.88% due January 2019 | Broadlands Village, The Glen and Kentlands Square I
Notes Payable [Line Items]
Principal and interest payments	$ 306,000
Balloon payment to be paid	$ 28,400,000
Amortization period	25 years
Number of shopping centers | shopping_center	3
Amortization of principal	$ 1,800,000
Fixed rate mortgage notes payable | 5.76% due May 2019
Notes Payable [Line Items]
Interest rate	5.76%
Fixed rate mortgage notes payable | 5.76% due May 2019 | Olde Forte Village
Notes Payable [Line Items]
Principal and interest payments	$ 98,000
Balloon payment to be paid	$ 9,000,000
Amortization period	25 years
Amortization of principal	$ 589,000
Fixed rate mortgage notes payable | 5.62% due July 2019
Notes Payable [Line Items]
Interest rate	5.62%
Fixed rate mortgage notes payable | 5.62% due July 2019 | Countryside
Notes Payable [Line Items]
Principal and interest payments	$ 133,000
Balloon payment to be paid	$ 12,300,000
Amortization period	25 years
Amortization of principal	$ 806,000
Fixed rate mortgage notes payable | 5.79% due September 2019
Notes Payable [Line Items]
Interest rate	5.79%
Fixed rate mortgage notes payable | 5.79% due September 2019 | Briggs Chancy MarketPlace
Notes Payable [Line Items]
Principal and interest payments	$ 133,000
Balloon payment to be paid	$ 12,200,000
Amortization period	25 years
Amortization of principal	$ 782,000
Fixed rate mortgage notes payable | 5.22% due January 2020
Notes Payable [Line Items]
Interest rate	5.22%
Fixed rate mortgage notes payable | 5.22% due January 2020 | Shops at Monocacy
Notes Payable [Line Items]
Principal and interest payments	$ 112,000
Balloon payment to be paid	$ 10,600,000
Amortization period	25 years
Amortization of principal	$ 696,000
Fixed rate mortgage notes payable | 5.60% due May 2020
Notes Payable [Line Items]
Interest rate	5.60%
Fixed rate mortgage notes payable | 5.60% due May 2020 | Boca Valley Plaza
Notes Payable [Line Items]
Principal and interest payments	$ 75,000
Balloon payment to be paid	$ 9,100,000
Amortization period	30 years
Amortization of principal	$ 329,000
Fixed rate mortgage notes payable | 5.30% due June 2020
Notes Payable [Line Items]
Interest rate	5.30%
Fixed rate mortgage notes payable | 5.30% due June 2020 | Palm Springs Center
Notes Payable [Line Items]
Principal and interest payments	$ 75,000
Balloon payment to be paid	$ 7,100,000
Amortization period	25 years
Amortization of principal	$ 453,000
Fixed rate mortgage notes payable | 5.83% due July 2020
Notes Payable [Line Items]
Interest rate	5.83%
Fixed rate mortgage notes payable | 5.83% due July 2020 | Thruway
Notes Payable [Line Items]
Principal and interest payments	$ 289,000
Balloon payment to be paid	$ 34,800,000
Amortization period	25 years
Amortization of principal	$ 1,200,000
Fixed rate mortgage notes payable | 5.81% due February 2021
Notes Payable [Line Items]
Interest rate	5.81%
Fixed rate mortgage notes payable | 5.81% due February 2021 | Jamestown Place
Notes Payable [Line Items]
Principal and interest payments	$ 66,000
Balloon payment to be paid	$ 6,100,000
Amortization period	25 years
Amortization of principal	$ 360,000
Fixed rate mortgage notes payable | 6.01% due August 2021
Notes Payable [Line Items]
Interest rate	6.01%
Fixed rate mortgage notes payable | 6.01% due August 2021 | Hunt Club Corners
Notes Payable [Line Items]
Principal and interest payments	$ 42,000
Balloon payment to be paid	$ 5,000,000
Amortization period	30 years
Amortization of principal	$ 159,000
Fixed rate mortgage notes payable | 5.62% due June 2022
Notes Payable [Line Items]
Interest rate	5.62%
Fixed rate mortgage notes payable | 5.62% due June 2022 | Landsowne Town Center
Notes Payable [Line Items]
Principal and interest payments	$ 230,000
Balloon payment to be paid	$ 28,200,000
Amortization period	30 years
Amortization of principal	$ 898,000
Fixed rate mortgage notes payable | 6.08% due September 2022
Notes Payable [Line Items]
Interest rate	6.08%
Fixed rate mortgage notes payable | 6.08% due September 2022 | Orchard Park
Notes Payable [Line Items]
Principal and interest payments	$ 73,000
Balloon payment to be paid	$ 8,600,000
Amortization period	30 years
Amortization of principal	$ 254,000
Fixed rate mortgage notes payable | 6.43% due April 2023
Notes Payable [Line Items]
Interest rate	6.43%
Fixed rate mortgage notes payable | 6.43% due April 2023 | BJs Wholesale
Notes Payable [Line Items]
Principal and interest payments	$ 80,000
Balloon payment to be paid	$ 9,300,000
Amortization period	30 years
Amortization of principal	$ 252,000
Fixed rate mortgage notes payable | 6.28% due February 2024
Notes Payable [Line Items]
Interest rate	6.28%
Fixed rate mortgage notes payable | 6.28% due February 2024 | Great Falls Shopping Center
Notes Payable [Line Items]
Principal and interest payments	$ 138,000
Balloon payment to be paid	$ 6,300,000
Amortization period	26 years
Amortization of principal	$ 824,000
Number of notes | note	3
Fixed rate mortgage notes payable | 7.35% due June 2024
Notes Payable [Line Items]
Interest rate	7.35%
Fixed rate mortgage notes payable | 7.35% due June 2024 | Leesburg Pike
Notes Payable [Line Items]
Principal and interest payments	$ 135,000
Balloon payment to be paid	$ 11,500,000
Amortization period	25 years
Amortization of principal	$ 465,000
Fixed rate mortgage notes payable | 7.60% due June 2024
Notes Payable [Line Items]
Interest rate	7.60%
Fixed rate mortgage notes payable | 7.60% due June 2024 | Village Center
Notes Payable [Line Items]
Principal and interest payments	$ 119,000
Balloon payment to be paid	$ 10,100,000
Amortization period	25 years
Amortization of principal	$ 394,000
Fixed rate mortgage notes payable | 7.02% due July 2024
Notes Payable [Line Items]
Interest rate	7.02%
Fixed rate mortgage notes payable | 7.02% due July 2024 | White Oak Shopping Center
Notes Payable [Line Items]
Principal and interest payments	$ 193,000
Balloon payment to be paid	$ 18,500,000
Amortization period	24 years 4 months 24 days
Loan amount			$ 10,500,000
Amortization of principal	$ 631,000
Fixed rate mortgage notes payable | 7.45% due July 2024
Notes Payable [Line Items]
Interest rate	7.45%
Fixed rate mortgage notes payable | 7.45% due July 2024 | Avenel Business Park
Notes Payable [Line Items]
Principal and interest payments	$ 246,000
Balloon payment to be paid	$ 20,900,000
Amortization period	25 years
Amortization of principal	$ 830,000
Fixed rate mortgage notes payable | 7.30% due January 2025
Notes Payable [Line Items]
Interest rate	7.30%
Fixed rate mortgage notes payable | 7.30% due January 2025 | Ashburn Village
Notes Payable [Line Items]
Principal and interest payments	$ 240,000
Balloon payment to be paid	$ 20,500,000
Amortization period	25 years
Amortization of principal	$ 797,000
Fixed rate mortgage notes payable | 6.18% due January 2026
Notes Payable [Line Items]
Interest rate	6.18%
Fixed rate mortgage notes payable | 6.18% due January 2026 | Ravenwood
Notes Payable [Line Items]
Principal and interest payments	$ 111,000
Balloon payment to be paid	$ 10,100,000
Amortization period	25 years
Amortization of principal	$ 424,000
Fixed rate mortgage notes payable | 5.31% due April 2026
Notes Payable [Line Items]
Interest rate	5.31%
Fixed rate mortgage notes payable | 5.31% due April 2026 | Clarendon Center
Notes Payable [Line Items]
Principal and interest payments	$ 753,000
Balloon payment to be paid	$ 70,500,000
Amortization period	25 years
Amortization of principal	$ 3,300,000
Fixed rate mortgage notes payable | 4.30% due October 2026
Notes Payable [Line Items]
Interest rate	4.30%
Fixed rate mortgage notes payable | 4.30% due October 2026 | Severna Park Market Place
Notes Payable [Line Items]
Principal and interest payments	$ 207,000
Balloon payment to be paid	$ 20,300,000
Amortization period	25 years
Amortization of principal	$ 1,100,000
Fixed rate mortgage notes payable | 4.53% due November 2026
Notes Payable [Line Items]
Interest rate	4.53%
Fixed rate mortgage notes payable | 4.53% due November 2026 | Kentlands Square II
Notes Payable [Line Items]
Principal and interest payments	$ 240,000
Balloon payment to be paid	$ 23,100,000
Amortization period	25 years
Amortization of principal	$ 1,200,000
Fixed rate mortgage notes payable | 4.70% due December 2026
Notes Payable [Line Items]
Interest rate	4.70%
Fixed rate mortgage notes payable | 4.70% due December 2026 | Cranberry Square
Notes Payable [Line Items]
Principal and interest payments	$ 113,000
Balloon payment to be paid	$ 10,900,000
Amortization period	25 years
Amortization of principal	$ 544,000
Fixed rate mortgage notes payable | 5.84% due May 2027
Notes Payable [Line Items]
Interest rate	5.84%
Fixed rate mortgage notes payable | 5.84% due May 2027 | Seven Corners
Notes Payable [Line Items]
Principal and interest payments	$ 463,200
Balloon payment to be paid	$ 42,300,000
Amortization period	25 years
Loan amount	$ 73,000,000
Amortization of principal	$ 1,700,000
Fixed rate mortgage notes payable | 4.04% due April 2028
Notes Payable [Line Items]
Interest rate	4.04%
Fixed rate mortgage notes payable | 4.04% due April 2028 | Hampshire Langley
Notes Payable [Line Items]
Principal and interest payments	$ 95,400
Balloon payment to be paid	$ 9,500,000
Amortization period	25 years
Amortization of principal	$ 493,000
Fixed rate mortgage notes payable | 3.51% due June 2028
Notes Payable [Line Items]
Interest rate	3.51%
Fixed rate mortgage notes payable | 3.51% due June 2028 | Beacon Center
Notes Payable [Line Items]
Balloon payment to be paid	$ 17,100,000
Amortization period	20 years
Amortization of principal	$ 1,800,000
Fixed rate mortgage notes payable | 3.99% due September 2028
Notes Payable [Line Items]
Interest rate	3.99%
Fixed rate mortgage notes payable | 3.99% due September 2028 | Seabreeze Plaza
Notes Payable [Line Items]
Principal and interest payments	$ 94,900
Balloon payment to be paid	$ 9,500,000
Amortization period	25 years
Amortization of principal	$ 488,000
Fixed rate mortgage notes payable | 3.69% Due March 2030
Notes Payable [Line Items]
Interest rate	3.69%
Fixed rate mortgage notes payable | 3.69% Due March 2030 | Shops at Fairfax and Boulevard
Notes Payable [Line Items]
Principal and interest payments	$ 153,300
Balloon payment to be paid	$ 15,500,000
Amortization period	25 years
Amortization of principal	$ 795,000
Fixed rate mortgage notes payable | 3.99% Due April 2030
Notes Payable [Line Items]
Interest rate	3.99%
Fixed rate mortgage notes payable | 3.99% Due April 2030 | Northrock
Notes Payable [Line Items]
Principal and interest payments	$ 84,400
Balloon payment to be paid	$ 8,400,000
Amortization period	25 years
Amortization of principal	$ 407,000
Fixed rate mortgage notes payable | 3.39% due January 2032
Notes Payable [Line Items]
Interest rate	3.39%
Fixed rate mortgage notes payable | 3.39% due January 2032 | Burtonsville Town Square
Notes Payable [Line Items]
Principal and interest payments	$ 198,000
Balloon payment to be paid	$ 20,300,000
Amortization period	25 years
Amortization of principal	$ 860,000
Fixed rate mortgage notes payable | 4.88% due September 2032
Notes Payable [Line Items]
Interest rate	4.88%
Fixed rate mortgage notes payable | 4.88% due September 2032 | Park Van Ness
Notes Payable [Line Items]
Principal and interest payments	$ 413,500
Balloon payment to be paid	$ 39,600,000
Amortization period	25 years
Amortization of principal	$ 369,000
Fixed rate mortgage notes payable | 3.75% due December 2032
Notes Payable [Line Items]
Interest rate	3.75%
Fixed rate mortgage notes payable | 3.75% due December 2032 | Washington Square
Notes Payable [Line Items]
Principal and interest payments	$ 308,000
Balloon payment to be paid	$ 31,100,000
Amortization period	25 years
Fixed rate mortgage notes payable | 8.00% due April 2034
Notes Payable [Line Items]
Interest rate	8.00%
Fixed rate mortgage notes payable | 8.00% due April 2034 | Olney
Notes Payable [Line Items]
Principal and interest payments	$ 60,400
Balloon payment to be paid	$ 14,700,000
Fixed rate increase on note	1.50%
Interest rate	8.00%
Negative amortization	$ (167,000)
Variable rate loans payable
Notes Payable [Line Items]
Interest rate spread on LIBOR	2.86%
Variable rate loans payable | Revolving credit facility
Notes Payable [Line Items]
Debt maturity extension period	1 year
Debt instrument fee	0.15%
Interest rate spread on LIBOR	1.45%
Variable rate loans payable | Metro Pike Center Bank Loan
Notes Payable [Line Items]
Interest rate spread on LIBOR	1.65%
Variable rate loans payable | Metro Pike Center Bank Loan | Metro Pike Center
Notes Payable [Line Items]
Principal and interest payments	$ 48,000
Balloon payment to be paid	14,200,000
Amortization of principal	$ 347,000