During the years ended December 31, 2020, 2019, and 2018, we made improvements, excluding tenant-funded improvements, to our properties totaling $11.6 million, $13.9 million and $56.3 million, respectively.

We committed $9.8 million for expenditures related to 0.1 million square feet of leases executed during 2020, excluding leasing activity for assets during the quarter in which the asset was sold or classified as held for sale. Committed but unspent tenant related obligations are leasing commissions and tenant improvements. Based on existing leases as of December 31, 2020, committed but unspent tenant related obligations were $9.6 million.

During the year ended December 31, 2020, we sold the following properties, which did not represent strategic shifts under ASC Topic 2015 (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 related to this property was $193.4 million, of which $194.7 million related to the gain on sale, $14.2 million and $12.8 million for the years ended December 31, 2020, 2019 and 2018, respectively.

During the year ended December 31, 2019, we sold the following properties, which did not represent strategic shifts under ASC Topic 2015 (dollars in thousands):


Property	Date Sold	Number of Properties	Number of Buildings	Square Footage	Gross Sale Price(1)		Gain on Sale
1735 Market Street(2)	March 2019	1	1	1,286,936	$	451,600	$	192,985
600 108th Avenue NE(3)	April 2019	1	1	254,510	195,000		149,009
Research Park(4)	June 2019	1	4	1,110,007	165,500		78,158
		3	6	2,651,453	$	812,100	$	420,152

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

(2)Certain of our subsidiaries sold 100.0% of the equity interests in the fee simple owner of this property. 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 related to this property was $0.1 million, $197.5 million, of which $193.0 million related to the gain on sale, and $8.5 million for the years ended December 31, 2020, 2019 and 2018 respectively.

(4)There was consideration of $2.0 million being held in escrow related to the sale of this property. In June 2020, these proceeds were released to the Company, and we recorded an additional $2.0 million gain on the sale for the year ended December 31, 2020.

During the year ended December 31, 2018, we sold the following properties, which did not represent strategic shifts under ASC Topic 2015 (dollars in thousands):


Property	Date Sold	Number of Properties	Number of Buildings	Square Footage	Gross Sale Price(1)		Gain (Loss) on Sale
1600 Market Street	February 2018	1	1	825,968	$	160,000	$	54,599
600 West Chicago Avenue(2)	February 2018	1	2	1,561,477	510,000		107,790
5073, 5075, & 5085 S. Syracuse Street	March 2018	1	1	248,493	115,186		42,762
1601 Dry Creek Drive	May 2018	1	1	552,865	68,500		26,979
777 East Eisenhower Parkway	August 2018	1	1	290,530	29,500		5,308
8750 Bryn Mawr Avenue	September 2018	1	2	636,078	141,000		15,194
97 Newberry Road	December 2018	1	1	289,386	7,100		(1,174)
		7	9	4,404,797	$	1,031,286	$	251,458

(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 continued operations for all periods presented through the date of sale. Net income for this property was $0.3 million, $0.3 million and $110.6 million, of which $107.8 million related to the gain on sale, for the years ended December 31, 2020, 2019 and 2018, 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 2021 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 FASB has issued additional guidance for companies to account for any COVID-19 related rent concessions in the form of FASB staff and board members’ remarks at the April 8, 2020 public meeting and the FASB staff question-and-answer document issued on April 10, 2020. We have elected the practical expedient to account for COVID-19 related rent concessions as if they were part of the enforceable rights and obligations of the parties under the existing lease contract. This policy has

been elected for our lessor portfolio for any rent deferrals, and we have elected to treat the related leases as if they are unchanged. For year ended December 31, 2020, we deferred collection of approximately $0.3 million of rental income on revenue that was recognized for the year ended December 31, 2020.

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, 2020 are as follows (in thousands):


	December 31,
	2020		2019		2018
Lease payments	$	40,514	$	81,698	$	129,539
Variable lease payments	21,620		35,171		54,829
Rental revenue	$	62,134	$	116,869	$	184,368