XML 82 R54.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Stockholders' and Mezzanine Equity - Additional Information (Detail) - USD ($) | 1 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jul. 31, 2017 | Feb. 29, 2016 | Feb. 29, 2012 | Sep. 30, 2017 | Jan. 11, 2017 | Dec. 31, 2016 | Jun. 30, 2016
Class of Stock [Line Items] |  |  |  |  |  |  |
Partnership units authorized (in shares) |  |  |  |  | 0 |  |
Mandatorily redeemable preferred stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  |  | 1,540,000 |  |  |  |
Series A and B Preferred Stock ATM Programs |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  |  |  | 2,264,000 |  | 2,264,000 |
Redeemable preferred stock (in shares) |  |  |  | 5,350,000 |  | 5,350,000 |
Series D Cumulative Redeemable Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  |  |  | 7.00% |  |  |
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer (as percent) |  |  |  | 90.00% |  |  |
Series C Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  |  | 7.125% |  |  |  |
Series C Preferred Stock | Mandatorily redeemable preferred stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock (in shares) |  |  |  |  | 0 | 160,000 |
Cantor Fitzgerald & Co | Common Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Maximum aggregate sales price of shares to be issued under open market sale agreement |  | $ 160,000,000.0 |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  |  |  | 1,500,000 |  |  |
Net proceeds from offering |  |  |  | $ 30,800,000 |  |  |
Maximum remaining capacity to sell preferred stock under open market sale agreement |  |  |  | $ 101,100,000 |  |  |
Cantor Fitzgerald & Co | Preferred Stock | Series A and B Preferred Stock ATM Programs |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  |  |  | 0 |  |  |
Maximum remaining capacity to sell preferred stock under open market sale agreement |  |  |  | $ 37,200,000 |  |  |
Cantor Fitzgerald & Co | Preferred Stock | Series A Cumulative Redeemable Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  | 7.75% |  |  |  |  |
Cantor Fitzgerald & Co | Preferred Stock | Series B Cumulative Redeemable Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Maximum aggregate sales price of shares to be issued under open market sale agreement |  | $ 40,000,000.0 |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  | 7.50% |  |  |  |  |
Cantor Fitzgerald & Co | Preferred Stock | Series D Cumulative Redeemable Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Maximum aggregate sales price of shares to be issued under open market sale agreement |  |  |  |  |  |  | $ 50,000,000.0
Maximum remaining capacity to sell preferred stock under open market sale agreement |  |  |  | $ 22,300,000 |  |  |
Overnight Offering |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Number of shares issued (in shares) | 1,200,000 |  |  |  |  |  |
Offering price (in dollars per share) | $ 20.52 |  |  |  |  |  |
Consideration received | $ 22,700,000 |  |  |  |  |  |
Over-Allotment Option |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Number of shares issued (in shares) | 200,000 |  |  |  |  |  |
Offering price (in dollars per share) | $ 20.52 |  |  |  |  |  |
Consideration received | $ 3,400,000 |  |  |  |  |  |
Series D Preferred Stock ATM Program | Series D Cumulative Redeemable Preferred Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Number of shares issued (in shares) |  |  |  | 400,000 |  |  |
Consideration received |  |  |  | $ 11,200,000 |  |  |

X
- Definition Maximum aggregate sales price of shares to be issued under open market sale agreement. + References No definition available. + Details
Name: | good_MaximumAggregateSalesPriceOfSharesToBeIssuedUnderOpenMarketSaleAgreement
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Maximum remaining capacity to sell preferred stock under open market sale agreement. + References No definition available. + Details
Name: | good_MaximumRemainingCapacityToSellPreferredStockUnderOpenMarketSaleAgreement
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Preferred Stock, Net Proceeds from Offering + References No definition available. + Details
Name: | good_PreferredStockNetProceedsfromOffering
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Temporary Equity, Contract Terms, Minimum Vote Needed to Trigger Change in Control From Tender Offer + References No definition available. + Details
Name: | good_TemporaryEquityContractTermsMinimumVoteNeededtoTriggerChangeinControlFromTenderOffer
Namespace Prefix: | good_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of authorized capital units or capital shares. This element is relevant to issuers of face-amount certificates and registered investment companies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04.16(a)) -URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996 + Details
Name: | us-gaap_CapitalUnitsAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- 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_ClassOfStockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage rate used to calculate dividend payments on preferred stock. + References No definition available. + Details
Name: | us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + References 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(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt. + References 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(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesIssued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Cash received on stock transaction after deduction of issuance costs. + References No definition available. + Details
Name: | us-gaap_SaleOfStockConsiderationReceivedOnTransaction
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The number of shares issued or sold by the subsidiary or equity method investee per stock transaction. + References No definition available. + Details
Name: | us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction. + References No definition available. + Details
Name: | us-gaap_SaleOfStockPricePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=us-gaap_MandatorilyRedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=good_SeriesAAndSeriesBPreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=good_SeriesDCumulativeRedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_SeriesCPreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=good_CantorFitzgeraldAndCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_PreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=good_SeriesACumulativeRedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=good_SeriesBCumulativeRedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=good_OvernightOfferingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=us-gaap_OverAllotmentOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=good_SeriesDPreferredStockATMProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |