The Company is engaged in the operation of shopping centers and other retail properties that are either owned or, with respect to certain shopping centers, operated under long-term ground leases that expire at various dates through June 20, 2066, with renewal options. Space in the shopping centers is leased to tenants pursuant to agreements that provide for terms ranging generally from one month to sixty years and generally provide for additional rents based on certain operating expenses as well as tenants’ sales volumes.

The Company leases land at six of its shopping centers, which are accounted for as operating leases and generally provide the Company with renewal options. Ground rent expense was $1.7 million, $1.4 million and $1.2 million (including capitalized ground rent at a property under development of $0, $0.1 million and $0.6 million) for the years ended December 31, 2018, 2017 and 2016 respectively. The leases terminate at various dates between 2020 and 2066. These leases provide the Company with options to renew for additional terms aggregating up to 22 years. The Company also leases space for its corporate office. Office rent expense under these leases was $1.0 million for each of the years ended December 31, 2018, 2017 and 2016, respectively.

During 2016, the Company entered into a 49-year master lease, which is accounted for as a capital lease. During the years ended December 31, 2018, 2017 and 2016, payments for this lease totaled $2.5 million, $2.5 million and $1.3 million, respectively. The property under the capital lease is included in Note 2.

The scheduled future minimum (i) rental revenues from rental properties under the terms of non-cancelable tenant leases greater than one year (assuming no new or renegotiated leases or option extensions for such premises) and (ii) rental payments under the terms of all non-cancelable operating and capital leases in which the Company is the lessee, principally for office space, land and equipment, as of December 31, 2018, are summarized as follows (in thousands):

Year Ending December 31,	Minimum Rental Revenues		Minimum Rental Payments
2019	$	187,158	$	4,775
2020		178,691		4,571
2021		159,749		4,354
2022		139,294		4,404
2023		121,456		4,425
Thereafter		513,853		180,618
Total	$	1,300,201	$	203,147

A ground lease expiring during 2078 provides the Company with an option to purchase the underlying land during 2031. If the Company does not exercise the option, the rents that will be due are based on future values and as such are not determinable at this time. Accordingly, the above table does not include rents for this lease beyond 2020.

During the years ended December 31, 2018, 2017 and 2016, no single tenant collectively comprised more than 10% of the Company’s consolidated total revenues.