Leases

We lease our corporate office in San Antonio, Texas, and we conduct our business operations through 29 other regional offices. Our regional operating locations typically include regional offices, storage and maintenance yards and personnel housing sufficient to support our operations in the area. We lease most of these properties, as well as office and other equipment, under non-cancelable and month to month operating leases, many of which contain renewal options and some of which contain escalation clauses. We recognize rent expense on a straight-line basis for our leases with escalating payments.

Rent expense under operating leases, including rental exit costs, was $5.4 million, $4.8 million and $5.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Future lease obligations required under non-cancelable operating leases as of December 31, 2018 were as follows (amounts in thousands):



Year ended December 31,
2019	$	3,318
2020	2,032
2021	1,721
2022	1,407
2023	1,110
Thereafter	1,738
	$	11,326