As of September 30, 2020, future lease payments related to our operating leases were as follows (in thousands):

Year ending December 31:	Operating Leases
Remaining 2020	$	6,088
2021		23,410
2022		19,696
2023		18,676
2024		16,362
2025		13,005
Thereafter		77,950
Total lease payments		175,187
Less: Imputed interest		(31,499	)
Total lease liability balance	$	143,688

During the third quarter of 2018, we executed an assignment of our Oxford office lease associated with our fourth quarter 2017 restructuring plan. The original lease term ends in November 2022. All terms under the original lease were assigned in full to the assignee, with the assignee becoming primarily liable to make rental payments directly to the landlord. Further, the assignee was required to provide the landlord a security deposit equal to twelve months rent to be used by the landlord in the event of the assignee’s non-performance.

In connection with the assignment, the Company became secondarily liable in the event the assignee is unable to perform under the lease. Based on the current rent and related payments, the maximum exposure to the Company is estimated to be $1.3 million as of September 30, 2020. However, the lease is subject to periodic rate reviews which allow the landlord to make market adjustments to the rent and other related payments and accordingly, the maximum exposure may be greater than this amount. As of September 30, 2020, the estimated fair value of this guarantee is not material.

Prior to July 1, 2019, the Company owned the building where its San Francisco headquarters is located and had operating lease arrangements with various third-party tenants for the remaining available office space. However, in connection with the sale and leaseback of the building, effective July 1, 2019 (the “Building Sale”), the Company sold all preexisting leases between the Company and its tenants to the buyer. As a result, all lessor related assets and liabilities were de-recognized upon closing.

For the nine months ended September 30, 2019 the components of lease income were as follows, which were recorded within other income (expense), net in our consolidated statement of operations (in thousands):

	Nine Months Ended September 30,
	2019
Operating lease income	$	10,563
Variable lease income		1,103
Total lease income	$	11,666