Commitments and Contingencies - Schedule of Total Lease Costs Associated With Operating and Finance Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Financing lease costs:
Total lease cost	$ 432	$ 409	$ 1,310	$ 1,297
Operating lease costs: \| Location, Statement of Financial Position, Activity, Accrual [Axis]: us-gaap:RealEstateInvestmentPropertyAtCost
Operating lease costs:
Operating lease	0	55	21	166
Income Statement Location: bnl:PropertyAndOperatingExpenses \| Operating lease costs:
Operating lease costs:
Operating lease	81	40	244	106
Income Statement Location: bnl:PropertyAndOperatingExpenses \| Ground Lease \| Operating lease costs:
Operating lease costs:
Operating lease	16	17	43	54
Income Statement Location: us-gaap:DepreciationAndAmortization \| Financing lease costs:
Financing lease costs:
Financing lease	14	14	41	36
Income Statement Location: us-gaap:GeneralAndAdministrativeExpense \| Operating lease costs:
Operating lease costs:
Operating lease	252	215	755	755
Income Statement Location: us-gaap:InterestExpenseNonoperating \| Financing lease costs:
Financing lease costs:
Financing lease	$ 69	$ 68	$ 206	$ 180