Fair Value of Assets and Liabilities - Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instruments
Senior Notes	$ 647,213	$ 646,844
Mortgage notes payable, net	$ 27,415	27,837
3.75% Senior unsecured note due In 2019
Fair Value of Financial Instruments
Interest rate (as a percent)	3.75%
5.875% Senior unsecured notes due In 2046
Fair Value of Financial Instruments
Interest rate (as a percent)	5.875%
5.88% interest rate, due in 2021
Fair Value of Financial Instruments
Interest rate (as a percent)	5.88%
7.00% interest rate, due in 2019
Fair Value of Financial Instruments
Interest rate (as a percent)	7.00%
8.15% Mortgage notes due in 2021
Fair Value of Financial Instruments
Interest rate (as a percent)	8.15%
Carrying Amount
Fair Value of Financial Instruments
Mortgage notes payable, net	$ 674,628	674,681
Carrying Amount \| 3.75% Senior unsecured note due In 2019
Fair Value of Financial Instruments
Senior Notes	347,238	346,952
Carrying Amount \| 5.875% Senior unsecured notes due In 2046
Fair Value of Financial Instruments
Senior Notes	299,975	299,892
Carrying Amount \| 5.88% interest rate, due in 2021
Fair Value of Financial Instruments
Mortgage notes payable, net	13,784	13,841
Carrying Amount \| 7.00% interest rate, due in 2019
Fair Value of Financial Instruments
Mortgage notes payable, net	8,683	8,778
Carrying Amount \| 8.15% Mortgage notes due in 2021
Fair Value of Financial Instruments
Mortgage notes payable, net	4,948	5,218
Fair Value
Fair Value of Financial Instruments
Mortgage notes payable, net	694,158	675,601
Fair Value \| 3.75% Senior unsecured note due In 2019
Fair Value of Financial Instruments
Senior Notes	355,248	354,078
Fair Value \| 5.875% Senior unsecured notes due In 2046
Fair Value of Financial Instruments
Senior Notes	310,000	292,268
Fair Value \| 5.88% interest rate, due in 2021
Fair Value of Financial Instruments
Mortgage notes payable, net	14,561	14,492
Fair Value \| 7.00% interest rate, due in 2019
Fair Value of Financial Instruments
Mortgage notes payable, net	9,063	9,188
Fair Value \| 8.15% Mortgage notes due in 2021
Fair Value of Financial Instruments
Mortgage notes payable, net	$ 5,286	$ 5,575

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
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

Name:	us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_SeniorSecuredNote3.75PercentDueIn2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_SeniorUnsecuredNotes5.875PercentDueIn2046Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote5.88PercentDueIn2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote7PercentDueIn2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote8.15PercentDueIn2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: