Leases

The Company is obligated under long-term real estate leases for corporate office space that was extended during the third quarter of 2015. Prior to this extension, the lease would have expired in October 2016, the lease is now set to expire in October 2022. In addition, the research lab space at CET, under an agreement amended in July 2012, is leased through April 2023, with an option to extend the lease through April 2028. The Company also subleases a portion of the space under these leases.

Rent expense is recognized over the expected term of the lease, including renewal option periods, if applicable, on a straight-line basis. Rent expense and sublease income were as follows for the years ended December 31:



	2017		2016		2015

Rent expense	$	1,074,437	$	1,150,614	$	978,591

Sublease income	$	573,494	$	646,235	$	550,452

Cumulative future minimum sublease income under noncancelable operating subleases totals approximately $0.6 million and will be paid through the leases ending in February 2019, March 2019, and October 2022. Future minimum lease payments under noncancelable operating leases (with initial or remaining lease terms in excess of one year) are as follows:



Year ending December 31:
2018	$	980,657
2019	959,902
2020	980,720
2021	1,001,603
2022 and thereafter	916,477
Total future minimum lease payments	$	4,839,359