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Indebtedness - Additional Information (Details)																		1 Months Ended	2 Months Ended	12 Months Ended
Indebtedness - Additional Information (Details)	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 ($)	Aug. 08, 2016 USD ($)	Oct. 30, 2015 USD ($)	Oct. 06, 2015 USD ($)	Sep. 01, 2015 USD ($)	Jul. 30, 2015 USD ($)	Jul. 10, 2015 USD ($) loan	Jul. 01, 2015 USD ($)	May 27, 2015 USD ($)	May 20, 2015 USD ($)	Jan. 31, 2018 USD ($)	Feb. 23, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	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]
Debt and credit facility repayments, including principal amortization																				$ 160,661,000	$ 186,533,000	$ 206,889,000
Loss on extinguishment of debt																				50,000	82,000	$ 512,000
Total principal balance																				523,412,000	527,082,000
Harding Place
Debt Instrument [Line Items]
Total principal balance																				$ 3,874,000	0
Harrisonburg Regal
Debt Instrument [Line Items]
Stated interest rate																				6.06%
Repayment of debt						$ 3,200,000
Total principal balance																				$ 0	3,256,000
Town Center Phase VI
Debt Instrument [Line Items]
Total principal balance																				$ 1,505,000	0
Hanbury Village
Debt Instrument [Line Items]
Stated interest rate																				3.78%						3.78%
Total principal balance																				$ 19,503,000	20,709,000
Sandbridge Commons
Debt Instrument [Line Items]
Repayment of debt				$ 700,000
Total principal balance																				$ 8,468,000	$ 9,376,000
The Cosmopolitan
Debt Instrument [Line Items]
Stated interest rate																				3.35%	3.75%				3.35%
Total principal balance																				$ 45,209,000	$ 45,884,000
Liberty Apartments
Debt Instrument [Line Items]
Stated interest rate																				5.66%
Repayment of debt			$ 5,000,000
Total principal balance																				$ 14,694,000	20,005,000
Lightfoot Marketplace
Debt Instrument [Line Items]
Total principal balance																				$ 10,500,000	12,194,000			$ 10,500,000
Smith’s Landing
Debt Instrument [Line Items]
Debt, face value																$ 21,600,000.0
Loss on extinguishment of debt																$ 100,000
Stated interest rate																4.05%				4.05%
Repayment of debt																$ 24,400,000
Total principal balance																				$ 19,764,000	20,511,000
Socastee Commons
Debt Instrument [Line Items]
Stated interest rate															4.57%					4.57%
Total principal balance																				$ 4,771,000	4,866,000
Acquisition, assumption of debt															$ 5,000,000
Columbus Village
Debt Instrument [Line Items]
Debt, face value														$ 8,800,000.0
Number of loans assumed \| loan														2
Johns Hopkins Village
Debt Instrument [Line Items]
Debt, face value													$ 50,000,000.0
Total principal balance																				$ 46,698,000	43,841,000
Oyster Point
Debt Instrument [Line Items]
Repayment of debt												$ 6,100,000
Subsequent Event \| Sandbridge Commons
Debt Instrument [Line Items]
Debt assumed, term																			5 years
LIBOR \| Harding Place
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																				2.95%
LIBOR \| Town Center Phase VI
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																				3.50%
LIBOR \| Sandbridge Commons
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																				1.75%
LIBOR \| Lightfoot Marketplace
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																				1.75%
LIBOR \| Columbus Village
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate														2.00%
LIBOR \| Johns Hopkins Village
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate													1.90%							1.90%
LIBOR \| Subsequent Event \| Sandbridge Commons
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate	1.75%
Note 5 \| North Point Center
Debt Instrument [Line Items]
Repayment of debt							$ 600,000
Total principal balance																				$ 0	643,000
Note 5 \| LIBOR \| North Point Center
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate																				2.00%
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]
Proceeds from new mortgage								$ 57,000,000
Debt assumed, term								5 years
Loss on extinguishment of debt																					100,000
Stated interest rate								3.25%
Construction Loans
Debt Instrument [Line Items]
Borrowings under construction loans																				$ 8,900,000	44,400,000
Construction Loans \| 595 King Street And 530 Meeting Street
Debt Instrument [Line Items]
Total principal balance																				$ 0
Construction Loans \| Whetstone Apartments
Debt Instrument [Line Items]
Loss on extinguishment of debt																	$ 100,000
Repayment of debt																	$ 17,800,000
Construction Loans \| Oceaneering
Debt Instrument [Line Items]
Loss on extinguishment of debt										$ 100,000
Repayment of debt										$ 18,700,000
Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate on credit facility as of end of period (as a percent)																				3.11%
Total principal balance																				$ 66,000,000	$ 107,000,000
Revolving Credit Facility \| Subsequent Event
Debt Instrument [Line Items]
Credit facility, increase in borrowings																		$ 58,000,000
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%
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)																				3.06%
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 [Member] \| Construction Loans \| Harding Place
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																												$ 29,800,000
Line of Credit [Member] \| Construction Loans \| 595 King Street And 530 Meeting Street
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																							$ 66,500,000
Operating Partnership \| Oyster Point
Debt Instrument [Line Items]
Debt, face value											$ 6,400,000.0
Operating Partnership \| Minimum \| Oyster Point
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate											1.40%
Operating Partnership \| Maximum \| Oyster Point
Debt Instrument [Line Items]
Stated interest rate, basis spread on variable rate											2.00%
Operating Partnership \| New Credit Facility
Debt Instrument [Line Items]
Aggregate capacity under the credit facility		$ 300,000,000
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
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 [Member] \| Construction Loans \| Town Center Phase VI
Debt Instrument [Line Items]
Aggregate capacity under the credit facility																											$ 27,900,000
Chesapeake, Virginia \| Commonwealth Of Virginia
Debt Instrument [Line Items]
Repayment of debt					$ 4,900,000