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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 |  |  |
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Apr. 01, 2015 | Mar. 03, 2015 | Jun. 24, 2014 | Feb. 27, 2013 | Dec. 31, 2016 | Nov. 30, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding debt |  |  |  |  |  | $ 907,800,000 |  |  |  |
Fixed rate mortgages |  |  |  |  |  | 783,400,000 |  |  | $ 796,169,000 |
Principal amount |  |  |  |  |  | 907,774,000 |  |  | 875,200,000 |
Debt outstanding with fixed-rate |  |  |  |  |  |  |  |  | 832,400,000 |
Debt outstanding with variable-rate |  |  |  |  |  |  |  |  | 42,800,000 |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  | 225,600,000 |  |  |  |
Letter of credit facility |  |  |  |  |  | 448,000 |  |  |  |
Guarantor obligations, maximum exposure |  |  |  |  |  | 51,000,000 |  |  | 51,000,000 |
Remaining loan balance |  |  |  |  |  | 231,800,000 |  |  |  |
Capitalization of debt issuance cost |  |  |  |  |  | 100,000 |  |  | 300,000 | $ 1,300,000
Beacon Center |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan amount |  |  |  |  |  |  |  | $ 11,250,000.00 |  |
Shops at Fairfax and Boulevard |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan term |  |  | 15 years |  |  |  |  |  |  |
Loan amount |  |  | $ 30,000,000 |  |  |  |  |  |  |
Loan fixed interest rate |  |  | 3.69% |  |  |  |  |  |  |
Northrock |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan term |  | 15 years |  |  |  |  |  |  |  |
Loan amount |  | $ 16,000,000 |  |  |  |  |  |  |  |
Loan fixed interest rate |  | 3.99% |  |  |  |  |  |  |  |
Metro Pike Center |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate spread on LIBOR |  |  |  |  | 1.65% |  |  |  |  |
Northrock |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate spread on LIBOR |  |  |  |  | 1.65% |  |  |  |  |
Revolving Credit Facility | Line of Credit |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding line of credit |  |  |  |  |  | $ 49,000,000 |  |  |  |
Unsecured Revolving Credit Facility |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  | $ 275,000,000.0 |  |  |  |  |  |
Extension in line of credit facility period |  |  |  | 1 year |  | 1 year |  |  |  |
Interest rate spread on LIBOR |  |  |  |  |  | 1.45% |  |  |  |
Unsecured Revolving Credit Facility | Minimum |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate spread on LIBOR |  |  |  |  |  | 1.45% |  |  |  |
Unsecured Revolving Credit Facility | Maximum |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate spread on LIBOR |  |  |  |  |  | 2.00% |  |  |  |
Fixed rate mortgage notes payable |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | $ 844,292,000 |  |  | 832,441,000 |
Fixed rate mortgage notes payable | Shops at Fairfax and Boulevard |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  |  | $ 15,500,000 |  |  |  |  |  |  |
Loan required periodic principal and interest payment |  |  | $ 153,300 |  |  |  |  |  |  |
Amortization schedule |  |  | 25 years |  |  |  |  |  |  |
Remaining loan balance |  |  | $ 15,200,000 |  |  |  |  |  |  |
Fixed rate mortgage notes payable | Northrock |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  | $ 8,400,000 |  |  |  |  |  |  |  |
Loan required periodic principal and interest payment |  | $ 84,400 |  |  |  |  |  |  |  |
Amortization schedule |  | 25 years |  |  |  |  |  |  |  |
Remaining loan balance |  | $ 14,500,000 |  |  |  |  |  |  |  |
Fixed rate mortgage notes payable | Metro Pike Center Bank Loan |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Guarantor obligations, maximum exposure |  |  |  |  |  | 7,800,000 |  |  |  |
Fixed rate mortgage notes payable | 5.84% due May 2027 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | 66,210,000 | [1] |  | 67,850,000 |
Fixed rate mortgage notes payable | 4.04% due April 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | 16,352,000 | [2] |  | 16,826,000 |
Fixed rate mortgage notes payable | 4.04% due April 2028 | Hampshire Langley |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  |  |  |  |  | 9,500,000 |  |  |  |
Loan required periodic principal and interest payment |  |  |  |  |  | $ 95,400 |  |  |  |
Principal amortization period |  |  |  |  |  | 25 years |  |  |  |
Fixed rate mortgage notes payable | 3.51% due June 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | $ 41,753,000 | [3] |  | 31,844,000 |
Fixed rate mortgage notes payable | 3.51% due June 2028 | Beacon Center |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  |  |  |  |  | 17,100,000 |  |  |  |
Loan required periodic principal and interest payment |  |  |  |  |  | $ 268,500 |  |  |  |
Principal amortization period |  |  |  |  |  | 20 years |  |  |  |
Fixed rate mortgage notes payable | 3.99% due September 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | $ 16,543,000 | [4] |  | 17,011,000 |
Fixed rate mortgage notes payable | 3.99% due September 2028 | Seabreeze Plaza |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  |  |  |  |  | 9,500,000 |  |  |  |
Loan required periodic principal and interest payment |  |  |  |  |  | $ 94,900 |  |  |  |
Principal amortization period |  |  |  |  |  | 25 years |  |  |  |
Fixed rate mortgage notes payable | 4.88% due September 2032 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Fixed rate mortgages |  |  |  |  |  | $ 70,144,000 | [5] |  | 45,208,000 |
Fixed rate mortgage notes payable | 4.88% due September 2032 | Park Van Ness |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan amount |  |  |  |  |  | 71,600,000 |  |  |  |
Loan required final principal payment |  |  |  |  |  | 39,600,000 |  |  |  |
Loan required periodic principal and interest payment |  |  |  |  |  | $ 413,500 |  |  |  |
Principal amortization period |  |  |  |  |  | 25 years |  |  |  |
Variable rate loans payable |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Variable rate debt |  |  |  |  |  | $ 63,482,000 |  |  | 42,801,000 |
Interest rate spread on LIBOR | [6] |  |  |  |  | 2.22% |  |  |  |
Variable rate loans payable | Unsecured Revolving Credit Facility |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Variable rate debt |  |  |  |  |  | $ 49,000,000 | [7] |  | 28,000,000 |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  | $ 275,000,000 |  |  |  |
Interest rate spread on LIBOR | [6] |  |  |  |  | 1.45% |  |  |  |
Variable rate loans payable | Metro Pike Center Bank Loan |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Variable rate debt |  |  |  |  |  | $ 14,482,000 | [8] |  | 14,801,000 |
Interest rate spread on LIBOR | [6] |  |  |  |  | 1.65% |  |  |  |
Variable rate loans payable | Metro Pike Center Bank Loan | Metro Pike Center |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Loan required final principal payment |  |  |  |  |  | $ 14,200,000 |  |  |  |
Loan required periodic principal and interest payment |  |  |  |  |  | 48,000 |  |  |  |
Debt Covenant |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Carrying value of properties collateralized |  |  |  |  |  | $ 957,200,000 |  |  | $ 856,800,000 |
Debt covenant, percentage of net proceeds of additional equity issuance |  |  |  |  |  | 80.00% |  |  |  |
Credit agreement leverage ratio |  |  |  |  |  | 60.00% |  |  |  |
Interest coverage ratio required minimum |  |  |  |  |  | 2.0 |  |  |  |
Required fixed charge coverage ratio |  |  |  |  |  | 1.3 |  |  |  |
Debt Covenant | Minimum |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Debt covenant required net assets |  |  |  |  |  | $ 542,100,000 |  |  |  |
[1] | 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 $1.6 million was amortized during 2016.
[2] | 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 $474,000 was amortized in 2016.
[3] | The loan is collateralized by Beacon Center and requires equal monthly principal and interest payments of $268,500 based upon a 20-year amortization schedule and a final payment of $17.1 million at loan maturity. Principal of $1.3 million was amortized in 2016.
[4] | 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 $468,000 was amortized in 2016.
[5] | 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.
[6] | Interest rate and scheduled maturity data presented as of December 31, 2016. Totals computed using weighted averages. Amounts shown are principal amounts and have not been reduced by any deferred debt issuance costs.
[7] | The loan is a $275.0 million unsecured revolving credit facility. Interest accrues at a rate equal to the sum of one-month LIBOR plus a spread of 145 basis points. The line may be extended at the Company’s option for one year with payment of a fee of 0.15%. Monthly payments, if required, are interest only and vary depending upon the amount outstanding and the applicable interest rate for any given month.
[8] | The loan is collateralized by Metro Pike Center and requires monthly principal and interest payments of approximately $48,000 and a final payment of $14.2 million at loan maturity. Principal of $319,000 was amortized during 2016.

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