Operating Leases

The Company's properties are leased to tenants under operating leases. Our leases for tenant space under 10,000 square feet generally have initial terms ranging from three to seven years. Leases greater than 10,000 square feet generally have initial lease terms in excess of five years, mostly comprised of anchor tenants. Many of the anchor leases contain provisions allowing the tenant the option of extending the term of the lease at expiration. Future minimum rents under non-cancelable operating leases as of December 31, 2018, excluding both tenant reimbursements of operating expenses and additional percentage rent based on tenants' sales, are as follows:



In Process Year Ending December 31,	Future Minimum Rents (in thousands)
2019	$	761,151
2020	693,848
2021	608,587
2022	516,369
2023	414,424
Thereafter	1,691,203
Total	$	4,685,582

The shopping centers' tenants primarily include national and regional supermarkets, drug stores, discount department stores, restaurants, and other retailers and, consequently, the credit risk is concentrated in the retail industry. Grocer anchor tenants represent approximately 18.0% of pro-rata annual base rent. There were no tenants that individually represented more than 5% of the Company's total annualized base rent.

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. Ground leases expire through the year 2101, and in most cases, provide for renewal options. Buildings and improvements constructed on the leased land are capitalized and depreciated over the shorter of the useful life of the improvements or the lease term.

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 most cases, provide for renewal options. Leasehold improvements are capitalized as tenant improvements, included in Other assets in the Consolidated Balance Sheets, and depreciated over the shorter of the useful life of the improvements or the lease term.

Operating lease expense under the Company's ground and office leases was $19.1 million, $18.4 million, and $13.1 million for the years ended December 31, 2018, 2017, and 2016, respectively. The following table summarizes the future obligations under non-cancelable operating leases as of December 31, 2018:



In Process Year Ending December 31,	Future Obligations (in thousands)
2019	$	15,077
2020	14,733
2021	13,893
2022	13,151
2023	12,558
Thereafter	467,706
Total	$	537,118