v3.21.2

Interest Rate Swaps - Summary of Interest-rate Swap Agreements (Detail) - Interest Rate Swap - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Derivative [Line Items] |  |
Derivative, Fixed rate | 2.11% |
Variable Rate Index | one-month LIBOR |
Notional Amount | $ 640,000 | $ 859,768
Fair Value | $ (36,196) | (72,103)
Wells Fargo Bank One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2021-02 |
Derivative, Fixed rate | 2.39% |
Notional Amount | $ 0 | 35,000
Fair Value | $ 0 | (70)
M&T Bank |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2021-08 |
Derivative, Fixed rate | 1.02% |
Notional Amount | $ 0 | 4,768
Fair Value | $ 0 | (25)
Capital One, National Association One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2021-12 |
Derivative, Fixed rate | 1.05% |
Notional Amount | $ 0 | 15,000
Fair Value | $ 0 | (141)
M&T Bank One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2022-09 |
Derivative, Fixed rate | 2.83% |
Notional Amount | $ 0 | 25,000
Fair Value | $ 0 | (1,139)
Bank of America |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2023-11 |
Derivative, Fixed rate | 2.80% |
Notional Amount | $ 0 | 25,000
Fair Value | $ 0 | (1,848)
M&T Bank Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2023-11 |
Derivative, Fixed rate | 2.65% |
Notional Amount | $ 0 | 25,000
Fair Value | $ 0 | (1,785)
Regions Bank |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2023-12 |
Derivative, Fixed rate | 1.18% |
Notional Amount | $ 0 | 25,000
Fair Value | $ 0 | (763)
Truist Financial Corporation One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2024-04 |
Derivative, Fixed rate | 1.99% |
Notional Amount | $ 0 | 25,000
Fair Value | $ 0 | (1,487)
Bank of Montreal One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2024-07 |
Derivative, Fixed rate | 1.16% |
Notional Amount | $ 0 | 40,000
Fair Value | $ 0 | (1,380)
Wells Fargo Bank Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2024-10 |
Derivative, Fixed rate | 2.72% |
Notional Amount | $ 15,000 | 15,000
Fair Value | $ (964) | (1,422)
Capital One, National Association Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2024-12 |
Derivative, Fixed rate | 1.58% |
Notional Amount | $ 15,000 | 15,000
Fair Value | $ (463) | (799)
Bank of Montreal Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2025-01 |
Derivative, Fixed rate | 1.91% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,044) | (1,725)
Truist Financial Corporation Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2025-04 |
Derivative, Fixed rate | 2.20% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,324) | (2,084)
Bank of Montreal Three |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2025-07 |
Derivative, Fixed rate | 2.32% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,478) | (2,351)
Truist Financial Corporation Three |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2025-07 |
Derivative, Fixed rate | 1.99% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,174) | (1,941)
Truist Financial Corporation Four |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2025-12 |
Derivative, Fixed rate | 2.30% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,546) | (2,481)
Bank of Montreal Four |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-01 |
Derivative, Fixed rate | 1.92% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,156) | (2,039)
Bank of Montreal Five |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-01 |
Derivative, Fixed rate | 2.05% |
Notional Amount | $ 40,000 | 40,000
Fair Value | $ (2,062) | (3,523)
Capital One, National Association Three |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-01 |
Derivative, Fixed rate | 2.08% |
Notional Amount | $ 35,000 | 35,000
Fair Value | $ (1,842) | (3,078)
Truist Financial Corporation Five |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-01 |
Derivative, Fixed rate | 1.93% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,164) | (2,019)
Capital One, National Association Four |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-04 |
Derivative, Fixed rate | 2.68% |
Notional Amount | $ 15,000 | 15,000
Fair Value | $ (1,204) | (1,843)
Capital One, National Association Five |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-07 |
Derivative, Fixed rate | 1.32% |
Notional Amount | $ 35,000 | 35,000
Fair Value | $ (682) | (1,806)
Bank of Montreal Six |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-12 |
Derivative, Fixed rate | 2.33% |
Notional Amount | $ 10,000 | 10,000
Fair Value | $ (692) | (1,156)
Bank of Montreal Seven |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2026-12 |
Derivative, Fixed rate | 1.99% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,300) | (2,372)
Wells Fargo Bank Three |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2027-04 |
Derivative, Fixed rate | 2.72% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (2,287) | (3,555)
Bank of Montreal Eight |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2027-12 |
Derivative, Fixed rate | 2.37% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,904) | (3,234)
Capital One, National Association Six |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2027-12 |
Derivative, Fixed rate | 2.37% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,909) | (3,199)
Wells Fargo Bank Four |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2028-01 |
Derivative, Fixed rate | 2.37% |
Notional Amount | $ 75,000 | 75,000
Fair Value | $ (5,743) | (9,650)
Bank of Montreal Nine |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2029-05 |
Derivative, Fixed rate | 2.09% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,557) | (2,994)
Regions Bank One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2029-05 |
Derivative, Fixed rate | 2.11% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,599) | (3,004)
Regions Bank Two |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2029-06 |
Derivative, Fixed rate | 2.03% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,459) | (2,843)
U.S. Bank National Association |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2029-06 |
Derivative, Fixed rate | 2.03% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (1,456) | (2,902)
U S Bank National Association One |  |
Derivative [Line Items] |  |
Derivative, Maturity date | 2029-08 |
Derivative, Fixed rate | 1.35% |
Notional Amount | $ 25,000 | 25,000
Fair Value | $ (187) | $ (1,445)

X
- Definition Date the derivative contract matures, in CCYY-MM format. + References No definition available. + Details
Name: | bnl_DerivativeMaturityYearAndMonth
Namespace Prefix: | bnl_
Data Type: | xbrli:gYearMonthItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
Name: | us-gaap_DerivativeFixedInterestRate
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959 + Details
Name: | us-gaap_DerivativeNotionalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Reference to the index or unit of measurement for the underlying which establishes the pricing terms of the derivative instrument. For example, the basis on the underlying for a natural gas futures contract might be the NYMEX price per million British thermal units (MMBtu). + References No definition available. + Details
Name: | us-gaap_DerivativeUnderlyingBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_WellsFargoBankOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_MAndTBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_MAndTBankOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfAmericaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_MAndTBankTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_RegionsBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_TruistFinancialCorporationOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_WellsFargoBankTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_TruistFinancialCorporationTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_TruistFinancialCorporationThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_TruistFinancialCorporationFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_TruistFinancialCorporationFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealSixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealSevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_WellsFargoBankThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_CapitalOneNationalAssociationSixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_WellsFargoBankFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_BankOfMontrealNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_RegionsBankOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_RegionsBankTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_USBankNationalAssociationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=bnl_USBankNationalAssociationOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |