We did not make any acquisitions during the years ended December 31, 2022, 2021 or 2020.

During the years ended December 31, 2022, 2021, and 2020, we made improvements, excluding tenant-funded improvements, to our properties totaling $4.0 million, $6.3 million and $11.6 million, respectively.

We committed $9.4 million for expenditures related to 0.2 million square feet of leases executed during 2022. Committed but unspent tenant related obligations are leasing commissions and tenant improvements. Based on existing leases as of December 31, 2022, committed but unspent tenant related obligations were $10.3 million.

During the year ended December 31, 2020, we sold the following properties, which did not represent strategic shifts under ASC Topic 205-20 (dollars in thousands):


Property	Date Sold	Number of Properties	Number of Buildings	Square Footage	Gross Sale Price(1)		Gain on Sale
109 Brookline Avenue	February 2020	1	1	285,556	$	270,000	$	225,190
333 108th Avenue NE(2)	March 2020	1	1	435,406	401,500		194,662
Georgetown-Green and Harris Buildings	May 2020	1	2	240,475	85,000		24,916
		3	4	961,437	$	756,500	$	444,768

(1)Gross sale price is before transfer taxes and credits, such as capital costs, contractual lease costs and rent abatements.

(2)The sale represents an individually significant disposition. The operating results of this property are included in continuing operations for all periods presented through the date of sale. Net income (loss) related to this property was $8,000, $(14,000) and $193.4 million, of which $194.7 million related to the gain on sale, for the years ended December 31, 2022, 2021 and 2020, respectively.

Our real estate properties are generally leased on gross lease and modified gross lease bases pursuant to non-cancelable, fixed term operating leases expiring between 2023 and 2035. These gross leases and modified gross leases require us to pay all or some property operating expenses and to provide all or some property management services. A portion of these property operating expenses are reimbursed by the tenants.

The future minimum lease payments, excluding tenant reimbursement revenue, scheduled to be received by us during the current terms of our leases as of December 31, 2022 are as follows (in thousands):


2023	$	36,557
2024	33,006
2025	29,949
2026	26,332
2027	20,645
Thereafter	44,870
	$	191,359

Rental revenue consists of the following (in thousands):


	December 31,
	2022		2021		2020
Lease payments	$	37,846	$	36,461	$	40,514
Variable lease payments	20,917		18,466		21,620
Rental revenue	$	58,763	$	54,927	$	62,134