Leases

We lease our corporate office facilities in San Antonio, Texas at a payment escalating from $42,511 per month in January 2016 to $50,246 per month in December 2020. We recognize rent expense on a straight-line basis for our corporate office lease. We also lease real estate at 43 other locations, which are primarily used for field offices and storage and maintenance yards, and we lease vehicles, office and other equipment under non-cancelable operating leases, most of which contain renewal options and some of which contain escalation clauses.

Future lease obligations required under non-cancelable operating leases as of December 31, 2015 were as follows (amounts in thousands):



Year ended December 31,
2016	$	3,618
2017	2,982
2018	2,347
2019	1,925
2020	1,187
Thereafter	445
	$	12,504

During 2015, we ceased use of several location offices which were under long-term leases and recognized an expense of $0.3 million in order to accrue the fair value of future lease obligations associated with the facilities which we are no longer using, in accordance with ASC Topic 420, Exit or Disposal Obligations. These accrued lease obligations which have been included in our current and long-term liabilities, according to the lease terms, are not reflected in the table above. Including the impact of lease termination penalties, total lease related exit costs incurred for the year ended December 31, 2015 was $0.5 million. Rent expense under operating leases, including rental exit costs, was $6.2 million, $5.9 million and $6.0 million for the years ended December 31, 2015, 2014 and 2013, respectively.