The Company generally leases its investment rental property to established tenants in the industrial, healthcare, restaurant, retail, and office property types. At September 30, 2022, the Company had 790 real estate properties, 777 of which were leased under leases that have been classified as operating leases, nine that have been classified as direct financing leases, one that has been classified as a sales-type lease, and three that were vacant. Of the nine leases classified as direct financing leases, three include land portions which are accounted for as operating leases. The sales-type lease includes a land portion which is accounted for as an operating lease. Most leases have initial terms of 10 to 20 years. The Company's leases generally provide for limited increases in rent as a result of fixed increases, increases in the Consumer Price Index ("CPI"), or increases in the tenant's sales volume. Generally, tenants are also required to pay all property taxes and assessments, substantially maintain the interior and exterior of the building, and maintain property and liability insurance coverage. The leases also typically provide for one or more multiple year renewal options, at the election of the tenant, and are subject to generally the same terms and conditions as the initial lease.

Depreciation expense on investment in rental property was as follows:


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(in thousands)	2022		2021		2022		2021
Depreciation	$	29,142	$	25,232	$	83,530	$	73,119

Estimated lease payments to be received under non-cancelable operating leases with tenants at September 30, 2022 are as follows:


(in thousands)
Remainder of 2022	$	91,352
2023		369,961
2024		369,585
2025		363,947
2026		354,818
Thereafter		2,941,041
	$	4,490,704

Since lease renewal periods are exercisable at the option of the tenant, the above amounts only include future lease payments due during the initial lease terms. Such amounts exclude any potential variable rent increases that are based on changes in the CPI or future variable rents which may be received under the leases based on a percentage of the tenant's gross sales. Additionally, certain of our leases provide tenants with the option to terminate their leases in exchange for termination penalties, or that are contingent upon the occurrence of a future event. Future lease payments within the table above have not been adjusted for these termination rights.

The Company's net investment in direct financing leases was comprised of the following:


(in thousands)	September 30, 2022			December 31, 2021
Undiscounted estimated lease payments to be received	$	39,032		$	42,602
Estimated unguaranteed residual values		14,547			15,203
Unearned revenue		(26,326	)		(28,893	)
Reserve for credit losses		(125	)		(130	)
Net investment in direct financing leases	$	27,128		$	28,782

Undiscounted estimated lease payments to be received under non-cancelable direct financing leases with tenants at September 30, 2022 are as follows:


(in thousands)
Remainder of 2022	$	763
2023		3,114
2024		3,171
2025		3,285
2026		3,357
Thereafter		25,342
	$	39,032

The above rental receipts do not include future lease payments for renewal periods, potential variable CPI rent increases, or variable percentage rent payments that may become due in future periods.

The following table summarizes amounts reported as Lease revenues, net on the Condensed Consolidated Statements of Income and Comprehensive Income:


	For the Three Months Ended September 30,					For the Nine Months Ended September 30,
(in thousands)	2022			2021		2022			2021
Contractual rental amounts billed for operating leases	$	91,208		$	78,886	$	263,109		$	227,142
Adjustment to recognize contractual operating lease billings on a straight-line basis		5,344			4,942		15,455			14,475
Net write-offs of accrued rental income		—			—		(1,326	)		(442	)
Variable rental amounts earned		309			130		786			335
Earned income from direct financing leases		719			726		2,163			2,184
Interest income from sales-type leases		14			14		43			43
Operating expenses billed to tenants		5,061			4,414		14,059			12,998
Other income from real estate transactions (a)		874			33,515		1,050			33,548
Adjustment to revenue recognized for uncollectible rental amounts billed, net		(5	)		150		39			(49	)
Total lease revenues, net	$	103,524		$	122,777	$	295,378		$	290,234