Debt Instrument, Amortization Period

No definition available.

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Balance Type:	na
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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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-Section 50
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+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments including both interest and principal payments.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of payment greater than the preceding installment payments to be paid at final maturity date of debt.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
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Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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+ Details

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Period Type:	instant

- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

+ Details

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- Definition

Amount, before accumulated depreciation, of real estate investment by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate. Excludes real estate not held as investment or interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Balance Type:	debit
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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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+ Details

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- Details

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Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Narrative (Details) - USD ($)					3 Months Ended	9 Months Ended
	Nov. 20, 2017	Sep. 01, 2017	Aug. 14, 2017	Jan. 18, 2017	Dec. 31, 2021	Sep. 30, 2018	Oct. 01, 2021	Oct. 01, 2020	Oct. 01, 2019	Jan. 26, 2018	Dec. 31, 2017	Jan. 31, 2017
Debt Instrument [Line Items]
Debt outstanding with fixed-rate						$ 870,901,000					$ 890,400,000
Principal amount						1,022,901,000					965,500,000
Debt outstanding with variable-rate						152,000,000					75,100,000
Outstanding line of credit						75,200,000					60,734,000
Carrying value of properties collateralizing mortgage notes						965,600,000					1,000,000,000
Final payment amount						760,955,000
Principal amount						1,012,912,000
Construction loan						861,897,000					897,888,000
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Outstanding line of credit						77,000,000					$ 61,000,000
Line of credit facility, remaining borrowing capacity						161,100,000
Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						185,000
New Facility \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity										$ 400,000,000
New Facility \| Term Loan \| Line of Credit
Debt Instrument [Line Items]
Outstanding line of credit						$ 75,000,000
Line of credit facility, maximum borrowing capacity										75,000,000
New Facility \| Term Loan \| LIBOR
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.30%
New Facility \| Term Loan \| LIBOR \| Minimum
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.30%
New Facility \| Term Loan \| LIBOR \| Maximum
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.90%
New Facility \| Revolving Line \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity										$ 325,000,000
New Facility \| Revolving Line \| LIBOR
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.35%
New Facility \| Revolving Line \| LIBOR \| Minimum
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.35%
New Facility \| Revolving Line \| LIBOR \| Maximum
Debt Instrument [Line Items]
Interest rate spread on LIBOR (percentage)						1.95%
Burtonsville Fixed Rate Mortgage
Debt Instrument [Line Items]
Debt instrument, term				15 years
Construction-to-permanent loan				$ 40,000,000								$ 40,000,000.0
Interest rate, stated percentage				3.39%
Periodic payment				$ 197,900
Amortization period				25 years
Final payment amount				$ 20,300,000
Glebe Road Construction Loan
Debt Instrument [Line Items]
Construction-to-permanent loan			$ 157,000,000.0
Interest rate, stated percentage			4.67%
Amortization period			25 years
Principal amount						$ 2,900,000
Park Van Ness Loan
Debt Instrument [Line Items]
Interest rate, stated percentage		4.88%
Periodic payment		$ 413,460
Amortization period		25 years
Final payment amount		$ 39,600,000
Guarantor obligations, maximum exposure						10,000,000
Construction loan						70,100,000
Washington Square 2017 Mortgage \| 3.75% due December 2032
Debt Instrument [Line Items]
Debt instrument, term	15 years
Construction-to-permanent loan	$ 60,000,000
Interest rate, stated percentage	3.75%
Periodic payment	$ 308,500
Amortization period	25 years
Final payment amount	$ 31,100,000
Kentlands Square II Bank Loan \| Fixed Rate Mortgage Notes Payable
Debt Instrument [Line Items]
Principal amount						35,600,000
Guarantor obligations, maximum exposure						$ 9,200,000
Forecast \| Glebe Road Construction Loan
Debt Instrument [Line Items]
Periodic payment					$ 887,900
Forecast \| Park Van Ness Loan
Debt Instrument [Line Items]
Guarantor obligations, maximum exposure							$ 0	$ 3,300,000	$ 6,700,000
Washington Square
Debt Instrument [Line Items]
Principal amount	$ 28,100,000