v3.21.2

Significant Accounting Policies - Summary of Impairment Charges (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) Property	Sep. 30, 2020 USD ($) Property	Sep. 30, 2021 USD ($) Property	Sep. 30, 2020 USD ($) Property
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties | Property	4	3	5	6
Impairment charge | $	$ 25,989	$ 14,732	$ 28,001	$ 17,399

X

- Definition

The number of individual properties owned.

+ References

No definition available.

+ Details

Name:	bnl_NumberOfIndividualProperties
Namespace Prefix:	bnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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

X

- Definition

The charge against earnings in the period to reduce the carrying amount of real property to fair value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

+ Details

Name:	us-gaap_ImpairmentOfRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration