We lease 391 retail sites from third parties under certain non-cancelable operating leases that expire from time to time through 2033. The weighted-average remaining lease term was 5.8 years as of December 31, 2019.

Lease expense for 2019 as measured under ASC 842 was classified in the statement of income as follows (in thousands):

Cost of sales	$	27,495
Operating expenses		379
General and administrative expenses		685
Total	$	28,559

Variable lease payments included in the above table are based on inflation, revenues or volumes and totaled $1.8 million for 2019. Short-term lease payments included in the table above that are excluded from the lease liability was $0.6 million for 2019. Cash paid for amounts included in the measurement of lease liabilities under operating leases totaled $25.8 million for 2019.

Lease expense as measured under ASC 840 was $21.5 million and $21.3 million for 2018 and 2017, respectively. Contingent rent expense, based on gallons sold, as measured under ASC 840 was $1.9 million for 2018 and 2017.

As of December 31, 2019, future minimum rental payments under operating leases, excluding variable lease payments or short-term payments, were as follows (in thousands). The weighted-average discount rate as of December 31, 2019 was 6.9%.

2020	$	24,359
2021		21,647
2022		20,055
2023		18,019
2024		15,712
Thereafter		66,063
Total future payments		165,855
Less impact of discounting		42,313
		123,542
Current portion		23,485
Long-term portion	$	100,057

Most lease agreements include provisions for renewals. We generally do not include renewal options in our lease term for purposes of measuring our lease liabilities and right-of-use assets unless the sublease to our customer extends beyond the term of the head lease.

Substantially all these retail sites are then subleased to lessee dealers (including DMS) or commission agents under leases with terms generally ranging from one to ten years and which may include renewal options. Sublease rental income amounted to $38.2 million for 2019.

Motor fuel stations are leased to tenants under operating leases with various expiration dates ranging through 2033. Most lease agreements include provisions for renewals. We generally do not include renewal options in our lease term. Future minimum rental payments under non-cancelable operating leases with third parties and DMS as of December 31, 2019 were as follows (in thousands):

	Third Party		DMS		Total
2020	$	58,561	$	4,886	$	63,447
2021		52,232		4,947		57,179
2022		42,123		5,018		47,141
2023		34,601		5,091		39,692
2024		32,317		5,165		37,482
Thereafter		77,377		18,383		95,760
Total future minimum lease payments	$	297,211	$	43,490	$	340,701

The future minimum rental payments presented above do not include contingent rent based on future inflation, future revenues or volumes of the lessee, or non-lease components for amounts that may be received as tenant reimbursements for certain operating costs.

Deferred rent income from straight-line rent relates to the cumulative amount by which straight-line rental income recorded to date exceeds cash rents billed to date under the lease agreement and totaled $7.1 million and $6.3 million at December 31, 2019 and 2018, respectively.