The Company generally leases its investment rental property to established tenants in the industrial, healthcare, restaurant, office, retail, and other industries. At December 31, 2019, the Company had 626 real estate properties which were leased under leases that have been classified as operating leases and 16 that have been classified as direct financing leases. Of the 16 leases classified as direct financing leases, four include land portions which are accounted for as operating leases (see Revenue Recognition within Note 2). Substantially all 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 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.

The Company’s leases do not include residual value guarantees. To protect the residual value of its assets under lease, the Company requires tenants to maintain certain levels of property insurance, and in some cases will purchase supplemental policies directly. Management physically inspects each property on a regular basis to ensure the tenant is maintaining the property so that it will be in a condition at the end of the lease term that is suitable for the Company to lease to a new tenant without the need for significant additional investment. For assets other than land, at lease inception the Company estimates the residual value taking into consideration the original fair value of the asset, less anticipated depreciation over the lease term. In general, at lease inception the Company assumes the value ascribed to land will be fully recoverable at the end of the lease term.

Rental property subject to non-cancelable operating leases with tenants are as follows:

	December 31,
(in thousands)	2019			2018
Land	$	548,911		$	411,043
Land improvements		275,470			239,701
Buildings and improvements		2,850,571			2,186,499
Equipment		11,492			11,492
		3,686,444			2,848,735
Less accumulated depreciation		(271,044	)		(206,989	)
	$	3,415,400		$	2,641,746

	For the years ended December 31,
(in thousands)	2019		2018		2017
Depreciation	$	83,797	$	66,055	$	50,360

Estimated lease payments to be received under non-cancelable operating leases with tenants at December 31, 2019 are as follows:

(in thousands)
2020	$	290,974
2021		295,713
2022		298,938
2023		302,017
2024		297,121
Thereafter		2,280,973
	$	3,765,736

Estimated minimum future rental receipts required under non-cancelable operating leases with tenants at December 31, 2018 are as follows:

(in thousands)
2019	$	231,725
2020		235,426
2021		238,223
2022		240,083
2023		241,498
Thereafter		2,007,118
	$	3,194,073

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. In addition, 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.

The Company’s net investment in direct financing leases is comprised of the following:

	December 31,
(in thousands)	2019			2018
Undiscounted estimated lease payments to be received	$	72,753		$	76,829
Estimated unguaranteed residual values		20,358			20,358
Unearned revenue		(51,221	)		(55,187	)
Net investment in direct financing leases	$	41,890		$	42,000

Undiscounted estimated lease payments to be received under non-cancelable direct financing leases with tenants at December 31, 2019 are as follows:

(in thousands)
2020	$	4,194
2021		4,283
2022		4,369
2023		4,456
2024		4,539
Thereafter		50,912
	$	72,753

Minimum future rental receipts required under non-cancelable direct financing leases with tenants at December 31, 2018 are as follows:

(in thousands)
2019	$	4,076
2020		4,194
2021		4,283
2022		4,369
2023		4,456
Thereafter		55,451
	$	76,829

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 on the Consolidated Statements of Income and Comprehensive Income:

	For the year ended
(in thousands)	December 31, 2019
Contractual rental amounts billed for operating leases	$	257,695
Adjustment to recognize contractual operating lease billings on a straight-line basis		22,109
Percentage rent income		152
Adjustment to revenue recognized for uncollectible rental amounts billed		(441	)
Total operating lease rental revenues		279,515
Earned income from direct financing leases		4,018
Operating expenses billed to tenants		14,614
Other income from real estate transactions		668
Total lease revenues	$	298,815