Mortgages Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Additional Information (Detail) (USD $)
 12 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2013
Minimum
Dec. 31, 2013
Maximum
Dec. 31, 2013
Kentlands Square II and Cranberry Square
Loan
Dec. 31, 2013
White Oak Shopping Center
Dec. 31, 2013
Metro Pike Center
Dec. 31, 2013
Northrock
Dec. 31, 2013
Cruse Market Place
Dec. 31, 2013
Beacon Center
Dec. 31, 2013
Northrock Loan
Dec. 31, 2013
Northrock Loan
Northrock
Dec. 31, 2013
5.31% due April 2026
Clarendon Center
Sep. 23, 2011
4.30% due October2026
Severna Park Market Place
Dec. 31, 2013
4.30% due October2026
Severna Park Market Place
Dec. 31, 2013
4.53% due November 2026
Kentlands Square II
Dec. 31, 2013
4.70% due December 2026
Cranberry Square
Dec. 31, 2013
5.84% due May 2027
Seven Corners Shopping Center
Dec. 31, 2013
4.04% due April 2028
Hampshire Langley
Dec. 31, 2013
3.51% due June 2028
Beacon Center
Dec. 31, 2013
3.99% due September 2028
Seabreeze Plaza
Oct. 25, 2013
4.88% due September 2032
Park Van Ness
Dec. 31, 2013
4.88% due September 2032
Park Van Ness
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
White Oak Shopping Center
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
Metro Pike Center bank loan
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
5.31% due April 2026
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
5.31% due April 2026
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
4.30% due October2026
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
4.30% due October2026
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
4.53% due November 2026
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
4.53% due November 2026
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
4.70% due December 2026
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
4.70% due December 2026
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
5.84% due May 2027
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
5.84% due May 2027
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
4.04% due April 2028
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
4.04% due April 2028
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
3.51% due June 2028
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
3.51% due June 2028
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
3.99% due September 2028
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
3.99% due September 2028
Dec. 31, 2013
Fixed Rate Mortgage Notes Payable
4.88% due September 2032
Dec. 31, 2012
Fixed Rate Mortgage Notes Payable
4.88% due September 2032
Dec. 31, 2013
Variable Rate Loans Payable
Dec. 31, 2012
Variable Rate Loans Payable
Dec. 31, 2013
Variable Rate Loans Payable
Northrock Loan
Dec. 31, 2012
Variable Rate Loans Payable
Northrock Loan
Dec. 31, 2013
Variable Rate Loans Payable
Metro Pike Center bank loan
Dec. 31, 2012
Variable Rate Loans Payable
Metro Pike Center bank loan
Dec. 31, 2013
Debt Covenant
Dec. 31, 2012
Debt Covenant
Dec. 31, 2013
Debt Covenant
Minimum
Dec. 31, 2013
Unsecured Revolving Credit Facility
Dec. 31, 2013
Unsecured Revolving Credit Facility
LIBOR
Dec. 31, 2013
Unsecured Revolving Credit Facility
LIBOR
Minimum
Dec. 31, 2013
Unsecured Revolving Credit Facility
LIBOR
Maximum
Debt Instrument [Line Items]                                                                                                                      
Fixed rate mortgages $ 820,068,000 $ 789,776,000                                             $ 789,872,000 $ 774,831,000     $ 118,128,000 [1] $ 120,822,000 $ 36,075,000 [2] $ 36,986,000 $ 40,974,000 [3] $ 41,970,000 $ 19,118,000 [4] $ 19,569,000 $ 70,856,000 [5] $ 72,233,000 $ 17,718,000 [6] $ 0 $ 34,391,000 [7] $ 0 $ 17,895,000 [8] $ 0 $ 0 [9] $ 0                          
Variable rate loans                                                                                             30,196,000 52,945,000 14,802,000 [10] 14,945,000 15,394,000 [11] 0              
Debt outstanding 820,068,000 827,800,000                                                                                                                  
Debt outstanding with fixed-rate   774,800,000                                                                                                                  
Debt outstanding with variable-rate   53,000,000                                                                                                                  
Line of credit facility, maximum borrowing capacity 164,200,000                                                                                                             175,000,000      
Line of credit facility maturity date                                                                                                               May 20, 2016      
Extension in line of credit facility period                                                                                                               1 year      
Letter of credit facility 628,229                                                                                                                    
Interest rate spread on LIBOR       1.60% 2.50%     1.65% 1.65%                                                                           1.65%   1.65%   1.65%                
Guarantor obligations, maximum exposure, percentage                       50.00%                                                                                              
Guarantor obligations, maximum exposure 51,000,000 51,000,000                   7,400,000                               7,700,000                                                              
Debt instrument maturity term 9 years 9 months 15 days [12]         6 months               15 years   15 years 15 years 15 years 15 years           10 years 1 month 0 days [12]                                           2 years 2 months 0 days [12]                        
Debt instrument amount           60,000,000 10,500,000 15,600,000 15,000,000         125,000,000   38,000,000 43,000,000 20,000,000 73,000,000 18,000,000 35,000,000 18,000,000   71,580,000                                                                      
Debt instrument, maturity year               2016 2016         2026   2026 2026 2026 2027 2028 2028 2028                                                                          
Debt instrument fixed interest rate             8.11%             5.31%   4.30% 4.53% 4.70% 5.84% 4.04% 3.51% 3.99%   4.88%                                                                      
Debt instrument required periodic principal and interest payment               48,000         47,000 753,000   207,000 240,000 113,000 463,200 95,400 203,200 94,900   413,500                                                                      
Principal amortization period             25 years 25 years 25 years   20 years     25 years 25 years 25 years 25 years 25 years 25 years 25 years 20 years 25 years 25 years 25 years                                                                      
Debt instrument required final principal payment             18,500,000 14,800,000 14,200,000       14,200,000 70,500,000   20,300,000 23,100,000 10,900,000 42,300,000 9,500,000 11,400,000 9,500,000 39,600,000                                                                        
Payments of debt financing costs                           104,200,000                                                                                          
Number of bridge financing loans           2                                                                                                          
Defeased mortgage loan 71,308,000 117,595,000 82,685,000                           40,000,000 20,000,000 63,000,000                                                                                
Proceeds from debt 101,600,000 83,500,000 286,000,000                               10,000,000                                                                                
Debt instrument fixed interest rate                                                     4.90%                                                                
Blended fixed interest rate             7.00%                                                                                                        
Line of credit facility, interest rate basis points                                                                                                                 1.60% 1.60% 2.50%
Debt instrument, term               3 years 3 years                     15 years 15 years 15 years                                                                          
Repayment of debt               15,900,000 15,000,000 6,900,000                       13,500,000                                                                          
Existing loan extension period                 2 years                                                                                                    
Payments of debt extinguishment costs                                           497,000                                                                          
Carrying value of properties collateralizing mortgage notes payable                                                                                                         907,200,000 916,100,000          
Limit in the amount of debt so as to maintain a gross asset value                                                                                                             503,300,000        
Percent of net proceeds from equity offerings                                                                                                         80.00%            
Leverage ratio                                                                                                         60.00%            
Interest coverage ratio                                                                                                         2.0            
Fixed charge coverage ratio                                                                                                         1.3            
Variable interest percent rate                                                                                                         40.00%            
Capitalization of debt issuance cost $ 3,200,000 $ 2,200,000 $ 1,400,000                                                                                                                
[1] The loan is collateralized by Clarendon Center and requires equal monthly principal and interest payments of $753,000 based upon a 25-year amortization schedule and a final payment of $70.5 million at loan maturity. Principal of $2.7 million was amortized during 2013.
[2] The loan is collateralized by Severna Park MarketPlace and requires equal monthly principal and interest payments of $207,000 based upon a 25-year amortization schedule and a final payment of $20.3 million at loan maturity. Principal of $911,000 was amortized during 2013.
[3] The loan is collateralized by Kentlands Square II and requires equal monthly principal and interest payments of $240,000 based upon a 25-year amortization schedule and a final payment of $23.1 million at loan maturity. Principal of $996,000 was amortized during 2013.
[4] The loan is collateralized by Cranberry Square and requires equal monthly principal and interest payments of $113,000 based upon a 25-year amortization schedule and a final payment of $10.9 million at loan maturity. Principal of $451,000 was amortized during 2013.
[5] The loan in the original amount of $73.0 million closed in May 2012, is collateralized by Seven Corners and requires equal monthly principal and interest payments of $463,200 based upon a 25-year amortization schedule and a final payment of $42.3 million at loan maturity. Principal of $1.4 million was amortized during 2013.
[6] The loan is collateralized by Hampshire Langley and requires equal monthly principal and interest payments of $95,400 based upon a 25 -year amortization schedule and a final payment of $9.5 million at loan maturity. Principal of $282,000 was amortized in 2013.
[7] The loan is collateralized by Beacon Center and requires equal monthly principal and interest payments of $203,200 based upon a 20-year amortization schedule and a final payment of $11.4 million at loan maturity. Principal of $609,000 was amortized in 2013.
[8] The loan is collateralized by Seabreeze Plaza and requires equal monthly principal and interest payments of $94,900 based upon a 25-year amortization schedule and a final payment of $9.5 million at loan maturity. Principal of $105,000 was amortized in 2013.
[9] The loan is a $71.6 million construction-to-permanent facility that is collateralized by and will finance a portion of the construction costs of Park Van Ness. During the construction period, interest will be funded by the loan. After conversion to a permanent loan, monthly principal and interest payments totaling $413,500 will be required based upon a 25-year amortization schedule. A final payment of $39.6 million will be due at maturity.
[10] The loan is collateralized by Northrock and requires monthly principal and interest payments of approximately $47,000 and a final payment of $14.2 million at maturity. Principal of $161,000 was amortized during 2013.
[11] The loan is collateralized by Metro Pike Center and requires monthly principal and interest payments of approximately $48,000 and a final payment of $14.8 million at loan maturity. Principal of $206,000 was amortized during 2013.
[12] Interest rate and scheduled maturity data presented as of December 31, 2013. Totals computed using weighted averages.