We lease office, retail and storage space to tenants, primarily under non-cancellable operating leases, which generally have terms ranging from five to fifteen years. Most of our leases provide tenants with extension options at either fixed or market rates and few of our leases provide tenants with options to early terminate, but such options generally impose an economic penalty on the tenant upon exercising. Rental revenue is recognized in accordance with ASC Topic 842, Leases, and includes (i) fixed payments of cash rents, which represents revenue each tenant pays in accordance with the terms of its respective lease and that is recognized on a straight-line basis over the non-cancellable term of the lease, and includes the effects of rent steps and rent abatements under the leases, (ii) variable payments of tenant reimbursements, which are recoveries of all or a portion of the operating expenses and real estate taxes of the property and is recognized in the same period as the expenses are incurred, (iii) amortization of acquired above and below-market leases, net and (iv) lease termination income.

	For the Three Months Ended March 31,
(Amounts in thousands)	2021		2020
Rental revenue:
Fixed	$	160,629	$	160,676
Variable		12,517		14,749
Total rental revenue	$	173,146	$	175,425

The following table is a schedule of future undiscounted cash flows under non-cancellable operating leases in effect as of March 31, 2021, for the nine-month period from April 1, 2021 through December 31, 2021 and each of the five succeeding years commencing January 1, 2022.

(Amounts in thousands)
2021	$	484,013
2022		625,476
2023		594,085
2024		566,940
2025		509,519
2026		414,600
Thereafter		1,927,623
Total	$	5,122,256