Commitments and Contingencies - Estimated Total Outstanding Commitments (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Tenant improvement allowances	$ 43,238
Reimbursable landlord work	6,906
Non-reimbursable landlord work	3,787
Leasing commissions	323
Total	$ 54,254

Lessor, Operating Lease, Commitment Outstanding, Non-Reimbursable Landlord Work

No definition available.

Name:	onl_LessorOperatingLeaseCommitmentOutstandingNonReimbursableLandlordWork
Namespace Prefix:	onl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant