Indebtedness - Additional Information (Details)																		12 Months Ended
	Oct. 12, 2018 USD ($)	Jul. 27, 2018 USD ($)	Jul. 12, 2018 USD ($)	Jun. 29, 2018 USD ($)	Jun. 14, 2018 USD ($)	Jun. 01, 2018 USD ($)	May 31, 2018 USD ($)	Mar. 27, 2018 USD ($)	Jan. 22, 2018	Oct. 26, 2017 USD ($) extension	Oct. 13, 2017 USD ($)	Aug. 10, 2017 USD ($)	Jul. 13, 2017 USD ($)	Apr. 07, 2017 USD ($)	Feb. 01, 2017 USD ($)	Aug. 30, 2016 USD ($)	Aug. 08, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 26, 2019 USD ($)	Jan. 31, 2019 USD ($)	Aug. 28, 2018 USD ($)	Mar. 28, 2018 USD ($)	Dec. 28, 2017 USD ($)	Nov. 01, 2017 USD ($)	Sep. 01, 2017	Aug. 09, 2017	Jun. 29, 2017 USD ($)	Feb. 24, 2017 USD ($)	Feb. 20, 2015 USD ($)
Debt Instrument [Line Items]
Total principal balances																		$ 700,722,000	$ 523,412,000
Debt and credit facility repayments, including principal amortization																		173,855,000	160,661,000	$ 186,533,000
Loss on extinguishment of debt																		11,000	$ 50,000	82,000
Sandbridge Commons
Debt Instrument [Line Items]
Repayment of debt												$ 700,000
Columbus Village
Debt Instrument [Line Items]
Repayment of debt								$ 8,300,000
Southgate Square
Debt Instrument [Line Items]
Debt, face value							$ 22,000,000
River City
Debt Instrument [Line Items]
Repayment of debt																		10,500,000
249 Central Park Retail, Fountain Plaza Retail, And South Retail
Debt Instrument [Line Items]
Debt, face value					$ 35,000,000
Johns Hopkins Village
Debt Instrument [Line Items]
Debt, face value		$ 53,000,000
Effective interest rate		4.19%
Lightfoot Marketplace
Debt Instrument [Line Items]
Total principal balances																										$ 10,500,000
Harrisonburg Regal
Debt Instrument [Line Items]
Repayment of debt														$ 3,200,000
Hanbury Village
Debt Instrument [Line Items]
Stated interest rate																												3.78%
The Cosmopolitan
Debt Instrument [Line Items]
Stated interest rate																			3.75%								3.35%
Liberty Apartments
Debt Instrument [Line Items]
Repayment of debt											$ 5,000,000
LIBOR | Sandbridge Commons
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate									1.75%
LIBOR | Southgate Square
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate							1.60%
LIBOR | River City
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate						1.50%
LIBOR | 249 Central Park Retail, Fountain Plaza Retail, And South Retail
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate					1.60%
LIBOR | Johns Hopkins Village
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate		1.25%
Note 5 | North Point Center
Debt Instrument [Line Items]
Repayment of debt															$ 600,000
New Retail Mortgage
Debt Instrument [Line Items]
Proceeds from new mortgage																	$ 35,000,000
Debt assumed, term																	5 years
Loss on extinguishment of debt																	$ 100,000
New Retail Mortgage | LIBOR
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																	1.95%
New Block 11 Mortgage
Debt Instrument [Line Items]
Stated interest rate																3.25%
Proceeds from new mortgage																$ 57,000,000
Debt assumed, term																5 years
Loss on extinguishment of debt																				100,000
Unsecured Debt
Debt Instrument [Line Items]
Total principal balances																		306,000,000	$ 216,000,000
Construction Loans
Debt Instrument [Line Items]
Borrowings under construction loans																		86,900,000	8,900,000	$ 44,400,000
Secured Debt
Debt Instrument [Line Items]
Total principal balances																		394,722,000	307,412,000
Secured Debt | Sandbridge Commons
Debt Instrument [Line Items]
Total principal balances																		8,258,000	8,468,000
Secured Debt | Southgate Square
Debt Instrument [Line Items]
Total principal balances																		21,442,000	20,708,000
Secured Debt | Market at Mill Creek
Debt Instrument [Line Items]
Total principal balances																		7,283,000	0
Secured Debt | Johns Hopkins Village
Debt Instrument [Line Items]
Total principal balances																		$ 52,708,000	46,698,000
Secured Debt | Lexington Square
Debt Instrument [Line Items]
Debt, face value																							$ 15,000,000
Stated interest rate																		4.50%					4.50%
Total principal balances																		$ 14,940,000	0
Secured Debt | Lightfoot Marketplace
Debt Instrument [Line Items]
Total principal balances																		$ 10,500,000	10,500,000
Secured Debt | Hanbury Village
Debt Instrument [Line Items]
Stated interest rate																		3.782%
Total principal balances																		$ 19,019,000	19,503,000
Secured Debt | The Cosmopolitan
Debt Instrument [Line Items]
Stated interest rate																		3.35%
Total principal balances																		$ 44,468,000	45,209,000
Secured Debt | Liberty Apartments
Debt Instrument [Line Items]
Stated interest rate																		5.66%
Total principal balances																		$ 14,437,000	14,694,000
Secured Debt | LIBOR | Sandbridge Commons
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.75%
Secured Debt | LIBOR | Southgate Square
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.60%
Secured Debt | LIBOR | Market at Mill Creek
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.55%
Secured Debt | LIBOR | Johns Hopkins Village
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.25%
Secured Debt | LIBOR | Lightfoot Marketplace
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.75%
Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate on credit facility as of end of period (as a percent)																		4.05%
Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Unused commitment fee																		0.15%
Revolving Credit Facility | Minimum | LIBOR
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.40%
Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Unused commitment fee																		0.25%
Revolving Credit Facility | Maximum | LIBOR
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		2.00%
Revolving Credit Facility | Unsecured Debt
Debt Instrument [Line Items]
Total principal balances																		$ 126,000,000	$ 66,000,000
Senior Unsecured Term Loan Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																															$ 50,000,000.0
Interest rate on credit facility as of end of period (as a percent)																		4.00%
Senior Unsecured Term Loan Facility | Minimum | LIBOR
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.35%
Senior Unsecured Term Loan Facility | Maximum | LIBOR
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																		1.95%
Line of Credit | Construction Loans | River City
Debt Instrument [Line Items]
Aggregate capacity under the credit facility						$ 16,300,000.0
Line of Credit | Construction Loans | Brooks Crossing
Debt Instrument [Line Items]
Aggregate capacity under the credit facility				$ 15,600,000.0
Line of Credit | Construction Loans | Market at Mill Creek
Debt Instrument [Line Items]
Aggregate capacity under the credit facility			$ 16,200,000.0
Line of Credit | Construction Loans | Greenside (Harding Place)
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																														$ 29,800,000.0
Line of Credit | Construction Loans | 595 King Street And 530 Meeting Street
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																									$ 66,500,000.0
Line of Credit | Construction Loans | LIBOR | Brooks Crossing
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate				1.60%
Line of Credit | Construction Loans | LIBOR | Market at Mill Creek
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate			1.55%
Line of Credit | Secured Debt | Lightfoot Marketplace
Debt Instrument [Line Items]
Aggregate capacity under the credit facility	$ 17,900,000.0
Proceeds from lines of credit	$ 10,500,000
Line of Credit | Secured Debt | Initial Tranche | Lightfoot Marketplace
Debt Instrument [Line Items]
Effective interest rate	4.77%
Line of Credit | Secured Debt | Initial Tranche | LIBOR | Lightfoot Marketplace
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate	1.75%
Operating Partnership | New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility										$ 300,000,000														$ 330,000,000
Operating Partnership | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																															150,000,000.0
Operating Partnership | Revolving Credit Facility | New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility										150,000,000.0
Accordion feature maximum borrowing capacity										$ 450,000,000.0
Number of extension options | extension										2
Duration of extension option										6 months
Extension fee percentage										0.075%
Operating Partnership | Senior Unsecured Term Loan Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																															$ 125,000,000.0
Operating Partnership | Senior Unsecured Term Loan Facility | New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility										$ 150,000,000														$ 180,000,000
249 Central Park Retail
Debt Instrument [Line Items]
Debt and credit facility repayments, including principal amortization																	$ 15,100,000
South Retail
Debt Instrument [Line Items]
Debt and credit facility repayments, including principal amortization																	6,700,000
Fountain Plaza Retail
Debt Instrument [Line Items]
Debt and credit facility repayments, including principal amortization																	$ 7,600,000
4525 Main Street
Debt Instrument [Line Items]
Debt and credit facility repayments, including principal amortization																$ 31,600,000
Encore Apartments
Debt Instrument [Line Items]
Debt and credit facility repayments, including principal amortization																$ 25,200,000
Virginia Beach, Virginia | Line of Credit | Construction Loans | Town Center Phase VI
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																													$ 27,900,000.0
Chesapeake, Virginia | Commonwealth Of Virginia
Debt Instrument [Line Items]
Repayment of debt													$ 4,900,000
Stabilization Of Property | Line of Credit | Secured Debt | Initial Tranche | Lightfoot Marketplace
Debt Instrument [Line Items]
Effective interest rate	4.62%
Stabilization Of Property | Line of Credit | Secured Debt | Initial Tranche | LIBOR | Lightfoot Marketplace
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate	1.60%
Subsequent Event | New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																						$ 355,000,000
Subsequent Event | Revolving Credit Facility | Unsecured Debt
Debt Instrument [Line Items]
Total principal balances																					$ 123,000,000
Subsequent Event | Senior Unsecured Term Loan Facility | New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																						$ 205,000,000