v3.21.2

Earnings per Share - Summary of Components used in Calculation of Basic and Diluted Earnings per Share (Parenthetical) (Detail) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Unvested restricted shares of common stock	374	341
Weighted average effects of OP Units outstanding	10,370	12,226

X

- Definition

Unvested restricted shares of common stock.

+ References

No definition available.

+ Details

Name:	bnl_UnvestedRestrictedSharesOfCommonStock
Namespace Prefix:	bnl_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Definition

The number of units or equivalent units outstanding for all classes.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187171-122770

+ Details

Name:	us-gaap_UnitsOfPartnershipInterestAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant