The Company's Lease income is comprised of both fixed and variable income, as follows:

Fixed and in-substance fixed lease income includes stated amounts per the lease contract, which are primarily related to base rent, and in some cases stated amounts for CAM, real estate taxes, and insurance. Income for these amounts is recognized on a straight line basis.

Variable lease income includes the following two main items in the lease contracts:

Recoveries from tenants represents amounts which tenants are contractually obligated to reimburse the Company for the tenants’ portion of actual Recoverable Costs incurred. Generally the Company’s leases provide for the tenants to reimburse the Company based on the tenants’ share of the actual costs incurred in proportion to the tenants’ share of leased space in the property.

Percentage rent represents amounts billable to tenants based on the tenants' actual sales volume in excess of levels specified in the lease contract.

The following table provides a disaggregation of lease income recognized under ASC Topic 842, Leases, as either fixed or variable lease income based on the criteria specified in ASC 842:

	Three months ended June 30, 2019			Six months ended June 30, 2019
Operating lease income
Fixed and in-substance fixed lease income	$	197,413			399,291
Variable lease income		62,610			125,445
Other lease related income, net
Above/below market rent amortization		6,793			20,247
Uncollectible amounts in lease income		(580	)		(1,444	)
Total lease income	$	266,236			543,539

Future minimum rents under non-cancelable operating leases, excluding variable lease payments, are as follows:

	Future Minimum Rents as of (in thousands)
Year Ending December 31,	June 30, 2019			December 31, 2018
2019	$	389,051	⁽¹⁾		761,151
2020		735,879			693,848
2021		653,515			608,587
2022		561,918			516,369
2023		460,749			414,424
Thereafter		1,841,436			1,691,203
Total	$	4,642,548			4,685,582

⁽¹⁾ The future minimum rental income for 2019 as of June 30, 2019 includes amounts due between July 1, 2019 and December 31, 2019.

The Company has shopping centers that are subject to non-cancelable, long-term ground leases where a third party owns the underlying land and has leased the land to the Company to construct and/or operate a shopping center.

The Company has 22 properties within its consolidated real estate portfolio that are either partially or completely on land subject to ground leases with third parties. Accordingly, the Company owns only a long-term leasehold or similar interest in these properties. These ground leases expire through the year 2101, and in most cases, provide for renewal options.

In addition, the Company has non-cancelable operating leases pertaining to office space from which it conducts its business. Office leases expire through the year 2029, and in many cases, provide for renewal options.

The ground and office lease expense is recognized on a straight line basis over the term of the leases, including management's estimate of expected option renewal periods. Operating lease expense under the Company's ground and office leases was as follows, including straight line rent expense and variable lease expenses such as CPI increases, percentage rent and reimbursements of landlord costs:

	Three months ended June 30, 2019		Six months ended June 30, 2019
Operating lease expense
Ground leases	$	3,528		7,200
Office leases		1,064		2,106
Total fixed operating lease expense		4,592		9,306
Variable lease expense
Ground leases		444		873
Office leases		131		274
Total variable lease expense		575		1,147
Total Lease Expense	$	5,167		10,453
Cash paid for amounts included in the measurement of operating lease liabilities
Operating cash flows from operating leases	$	3,721		7,412

Operating lease expense under the Company's ground and office leases was $5.2 million and $5.0 million during the three months ended June 30, 2019 and 2018, respectively, and $10.5 million and $9.2 million during the six months ended June 30, 2019 and 2018, respectively, which includes fixed and variable rent expense.

The following table summarizes the undiscounted future cash flows by year attributable to the operating lease liabilities under ground and office leases as of June 30, 2019, and provides a reconciliation to the Lease liability included in the accompanying Consolidated Balance Sheets:

	Lease liabilities (in thousands)
Year Ending December 31,	Ground Leases			Office Leases			Total
2019 ⁽¹⁾	$	5,336			2,522			7,858
2020		10,706			4,976			15,682
2021		10,674			3,863			14,537
2022		10,698			2,893			13,591
2023		10,914			2,188			13,102
Thereafter		564,081			5,955			570,036
Total undiscounted lease liabilities	$	612,409			22,397			634,806
Present value discount		(408,464	)		(2,383	)		(410,847	)
Lease liabilities	$	203,945			20,014			223,959
Weighted average discount rate	5.2%			4.0%
Weighted average remaining term	49.6 years			5.7 years

⁽¹⁾ The undiscounted lease liability maturities shown for 2019 are as of June 30, 2019, and includes amounts due between July 1, 2019 and December 31, 2019.

The following table summarizes the future obligations under non-cancelable operating leases, excluding unexercised renewal options, as of December 31, 2018:

	Future Lease Obligations (in thousands)
Year Ending December 31,	Ground Leases		Office Leases		Total Future Lease Obligations
2019	$	10,672		4,405		15,077
2020		10,439		4,294		14,733
2021		10,344		3,549		13,893
2022		10,258		2,893		13,151
2023		10,369		2,189		12,558
Thereafter		461,762		5,944		467,706
Total	$	513,844		23,274		537,118