v3.21.2

Acquisitions of Rental Property - Acquisitions of Rental Property Closed - (Detail) $ in Thousands |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 9 Months Ended |
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Oct. 27, 2021 USD ($) Property | Oct. 22, 2021 USD ($) Property | Oct. 01, 2021 USD ($) Property | Sep. 30, 2021 USD ($) Property | Sep. 29, 2021 USD ($) Property | Sep. 24, 2021 USD ($) Property | Sep. 17, 2021 USD ($) Property | Sep. 08, 2021 USD ($) Property | Aug. 23, 2021 USD ($) Property | Jul. 30, 2021 USD ($) Property | Jul. 29, 2021 USD ($) Property | Jul. 21, 2021 USD ($) Property | Jul. 02, 2021 USD ($) | Jun. 30, 2021 USD ($) Property | Jun. 28, 2021 USD ($) Property | Jun. 25, 2021 USD ($) Property | Jun. 09, 2021 USD ($) Property | Jun. 04, 2021 USD ($) Property | Mar. 31, 2021 USD ($) Property | Mar. 30, 2021 USD ($) Property | Mar. 11, 2021 USD ($) Property | Feb. 26, 2021 USD ($) | Feb. 05, 2021 USD ($) Property | Oct. 31, 2021 USD ($) Property | Sep. 30, 2021 USD ($) Property | Sep. 30, 2020 Property
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type | [1] |  |  |  |  |  |  |  |  |  |  |  |  | Industrial |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  |  |  | 80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 80 | 0
Real Estate Acquisition Price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 511,704 |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |
Real Estate Acquisition Price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12,970 |  |
Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  |  |  |  |  |  |  |  | Healthcare |  |  |  |  |  | Healthcare | Healthcare |  |  |  | Healthcare |  |  |  | Healthcare |  |  |
Number of Properties | Property |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  | 7 | 4 |  |  |  | 3 |  |  |  | 1 |  |  |
Real Estate Acquisition Price |  |  |  |  |  |  |  |  |  | $ 60,000 |  |  |  |  |  | $ 30,750 | $ 15,300 |  |  |  | $ 14,140 |  |  |  | $ 4,843 |  |  |
Healthcare | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  |  | Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Acquisition Price |  |  |  | $ 3,306 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restaurant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Restaurant |  |  |  |
Real Estate Acquisition Price | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 181 |  |  |  |
Retail |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  |  |  |  |  | Retail | Retail | Retail |  |  | Retail | Retail |  |  | Retail |  | Retail |  | Retail |  | Retail | Retail |  |  |  |  |
Number of Properties | Property |  |  |  |  |  |  | 1 | 1 | 2 |  |  | 3 | 1 |  |  | 1 |  | 8 |  | 2 |  | 11 | 13 |  |  |  |  |
Real Estate Acquisition Price |  |  |  |  |  |  | $ 2,456 | $ 1,722 | $ 8,901 |  |  | $ 4,586 | $ 5,565 |  |  | $ 1,279 |  | $ 12,131 |  | $ 19,420 |  | $ 41,324 | $ 26,834 |  |  |  |  |
Retail | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  | Retail |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties | Property |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Acquisition Price |  | $ 4,278 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Industrial |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  |  |  | Industrial |  | Industrial |  |  |  | Industrial |  |  |  |  |  |  |  | Industrial |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  |  |  | 3 |  | 2 |  |  |  | 2 |  |  |  |  |  |  |  | 11 |  |  |  |  |  |  |  | 3 |
Real Estate Acquisition Price |  |  |  |  | $ 59,343 |  | $ 48,699 |  |  |  | $ 11,011 |  |  | $ 4,500 | [1] |  |  |  | $ 106,578 |  |  |  |  |  |  |  |  |
Industrial | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  | Industrial |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Acquisition Price |  |  | $ 5,386 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Industrial |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Type |  |  |  |  |  | Industrial |  |  |  |  |  | Industrial |  |  |  |  |  |  | Industrial |  |  |  |  |  |  |  |  |
Number of Properties | Property |  |  |  |  |  | 1 |  |  |  |  |  | 1 |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |
Real Estate Acquisition Price |  |  |  |  |  | $ 10,600 |  |  |  |  |  | $ 13,041 |  |  |  |  |  |  | $ 8,500 |  |  |  |  |  |  |  |  |
[1] | Acquisition of land related to an existing property
[2] | Acquisition of additional land adjacent to an existing property

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- Definition The number​ of rental​ properties acquired. + References No definition available. + Details
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Namespace Prefix: | bnl_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Property type. + References No definition available. + Details
Name: | bnl_PropertyType
Namespace Prefix: | bnl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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- Definition The cash outflow from the acquisition of a piece of land, anything permanently fixed to it, including buildings, structures on it and so forth; includes real estate intended to generate income for the owner; excludes real estate acquired for use by the owner. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RealEstatePropertiesAxis=bnl_RestaurantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RealEstatePropertiesAxis=us-gaap_RetailMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RealEstatePropertiesAxis=srt_IndustrialPropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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