(6) Commitments

As of December 31, 2017, Forrester had future contractual obligations as follows for operating leases (in thousands):

2018	$	12,506
2019		11,442
2020		10,835
2021		9,409
2022		8,001
Thereafter		29,490
Total minimum lease payments	$	81,683

The cost of these operating leases, including any contractual rent increases, rent concessions, and landlord incentives, are recognized ratably over the life of the related lease agreement. Aggregate rent expense was $17.4 million, $16.1 million and $16.0 million for the years ended December 31, 2017, 2016, and 2015, respectively.