10. Commitments and Contingencies Operating Leases  The Company has operating lease agreements for offices in the United States, Hungary, Australia, the United Kingdom, Ireland and India that expire at various dates through 2028. In December 2015, the Company amended its current lease for its Budapest, Hungary office space to provide for an expansion of leased space and to extend the term of the lease. The term of the amended lease began in June 2016 and extends through June 2021. The aggregate amount of minimum lease payments to be made over the term of the lease is approximately $8.3 million (EUR 7.5 million). The lease agreement required a bank guarantee of $0.5 million (EUR 0.5 million). The bank guarantee is classified as restricted cash. In December 2014, the Company entered into a lease for new office space in Boston, Massachusetts which began in December 2015 and extends through June 2028. The aggregate amount of minimum lease payments to be made over the term of the lease is approximately $47.0 million. Pursuant to the terms of the lease, the landlord was responsible for making certain improvements to the leased space up to an agreed upon cost to the landlord. Any excess costs for these improvements will be billed by the landlord to the Company as additional rent. These excess costs total $3.4 million, all of which were paid as of June 30, 2016. The lease required a security deposit of $3.3 million in the form of an irrevocable, unsecured standby letter of credit. The lease includes an option to extend the original term of the lease for two successive five year periods. Rent expense under all leases was $1.9 million and $3.0 million for the three months ended June 30, 2015 and 2016, respectively, and $3.8 million and $5.9 million for the six months ended June 30, 2015 and 2016, respectively. The Company records rent expense on a straight-line basis for leases with scheduled escalation clauses or free rent periods. The Company also enters into hosting services agreements with third-party data centers and