7. Commitments and Contingencies Lease Commitments The Company has various non -cancelable long -term operating leases. The approximate minimum annual rental payments due under these lease agreements as of December 31 , 2014 are presented in the following table. 2015 $ 4,004 2016 4,006 2017 3,946 2018 3,915 2019 123 Total minimum lease payments $ 15,994 Certain lease agreements contain renewal options and, in addition to the minimum annual rentals, generally provide for payment of a share of the real estate taxes and operating expenses in excess of a base amount. Rental expense was $4,236 , $4,150 , and $4,114 for the years ended December 31 , 2014 , 2013 , and 2012 , respectively. All leases expire prior to 2020. The Company expects that in the normal course of business, leases that expire will be renewed. An eighth amendment to a lease agreement for the lease of office space was executed on April 5, 2007. Under the provisions of this amendment, additional space was occupied and the lease term was extended an additional ten years commencing on January 1, 2009 , with an option to renew for one additional five -year term. At December 31, 2014, the Company has software purchase commitments of $1,409 . As part of the Company s investment activity, we have committed $25,000 to investments in limited partnerships. The Company has contributed $10,576 to these commitments as of December 31, 2014. As of December 31, 2014, the remaining committed capital due to be called is $14,424 . Contingencies Various claims, generally incidental to the conduct of normal business, are pending or alleged against the Company from time to time. In the opinion of management, based in part on the advice of legal counsel, the ultimate resolution of such claims will not have a material adverse effect on the Company s consolidated financial statements. However, if estimates of the ultimate resolutions of those proceedings are revised, liabilities related to those proceedings could be adjusted in the near term. Massachusetts law requires that