XML 72 R51.htm IDEA: XBRL DOCUMENT
v3.20.2

Equity and Mezzanine Equity - Additional Information (Detail) - USD ($) |  | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Feb. 20, 2020 | Jun. 30, 2020 | Feb. 19, 2020 | Jan. 29, 2020 | Dec. 31, 2019 | Jan. 11, 2019
Class of Stock [Line Items] |  |  |  |  |  |
Common stock, shares outstanding (in shares) | 60,290,000 | 33,960,707 | 86,290,000 |  | 32,593,651 |
Series D Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer (as percent) |  | 90.00% |  |  |  |
Preferred Stock | Series D Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  | 7.00% |  |  |  |
Preferred Stock | Series E Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) |  | 6.625% |  |  |  |
Preferred Stock | Series F Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, dividend rate percentage (as percent) | 6.00% |  |  |  |  |
Redeemable preferred stock, shares authorized (in shares) | 26,000,000 |  |  |  |  |
Redeemable preferred stock, shares outstanding (in shares) |  | 0 |  |  |  |
Baird, Goldman Sachs, Stifel, Fifth Third, and U.S. Bancorp Investments, Inc. | Preferred Stock | Series E Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  | 86,564 |  |  |  |
Consideration received |  | $ 1,900,000 |  |  |  |
Maximum aggregate sales price of shares to be issued under open market sale agreement |  | 100,000,000.0 |  |  |  |
Maximum remaining capacity to sell common stock under open market sale agreement |  | $ 98,000,000.0 |  |  |  |
Common Stock ATM Program | Baird, Goldman Sachs, Stifel, Fifth Third, and U.S. Bancorp Investments, Inc. | Common Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) |  | 1,300,000 |  |  |  |
Consideration received |  | $ 28,400,000 |  |  |  |
Maximum aggregate sales price of shares to be issued under open market sale agreement |  | 250,000,000.0 |  |  |  |
Maximum remaining capacity to sell common stock under open market sale agreement |  | 208,700,000 |  |  |  |
2019 Universal Shelf |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized |  | 407,200,000 |  |  |  | $ 500,000,000.0
2020 Universal Shelf |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized |  | $ 800,000,000.0 |  | $ 800,000,000.0 |  |
2020 Universal Shelf | Preferred Stock | Series F Cumulative Redeemable Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized |  |  |  | $ 636,500,000 |  |

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 Common Stock Under Open Market Sale Agreement + References No definition available. + Details
Name: | good_MaximumRemainingCapacityToSellCommonStockUnderOpenMarketSaleAgreement
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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 Universal Registration Statement, Amount Authorized + References No definition available. + Details
Name: | good_UniversalRegistrationStatementAmountAuthorized
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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 Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_CommonStockSharesOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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://fasb.org/us-gaap/role/ref/legacyRef -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=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesOutstanding
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
- Details
Name: | us-gaap_StatementClassOfStockAxis=good_SeriesDCumulativeRedeemablePreferredStockMember
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_SeriesECumulativeRedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_CounterpartyNameAxis=good_BairdGoldmanSachsStifelFifthThirdandU.S.BancorpInvestmentsInc.Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=good_CommonStockATMProgramMember
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_SubsidiarySaleOfStockAxis=good_A2019UniversalShelfMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=good_A2020UniversalShelfMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |