Commitments and Contingencies Leases The Company rents office space under leases that expire at various dates through 2030 . Future annual minimum lease commitments under operating leases were as follows: Years ending December 31: 2019 $ 15,997 2020 15,437 2021 14,705 2022 10,816 2023 9,910 Thereafter 39,449 Total $ 106,314 Rent expense for all operating leases totaled: Year Ended December 31, 2018 2017 2016 Rent expense $ 19,658 $ 18,084 $ 14,984 Purchase Obligations and Indemnifications The Company includes various types of indemnification and guarantee clauses in certain arrangements. These indemnifications and guarantees may include, but are not limited to, infringement claims related to intellectual property, direct or consequential damages and guarantees to certain service providers and service level requirements with certain customers. The type and amount of any potential indemnification or guarantee varies substantially based on the nature of each arrangement. The Company has experienced no previous claims and cannot determine the maximum amount of potential future payments, if any, related to such indemnification and guarantee provisions. The Company believes that it is unlikely it will have to make material payments under these arrangements and therefore has not recorded a contingent liability in the consolidated balance sheets. The Company enters into unconditional purchase obligations arrangements for certain of its services that it receives in the normal course of business. As of December 31, 2018 , the Company estimated future minimum unconditional purchase obligations of $41,112 . Legal Proceedings The Company is involved in legal proceedings arising in the ordinary course of its business. Legal fees and other costs associated with such actions are expensed as incurred. The Company will record a provision for these claims when it is both probable that a liability has been incurred and the amount of the loss, or a range of the potential loss, can be reasonably estimated. These provisions are reviewed regularly and adjusted to reflect the impacts of negotiations, settlements, rulings, advice of legal counsel, and other information or events pertaining to a particular case. Legal proceedings accruals are recorded when and if it is determined that a loss is both probable and reasonably estimable. For litigation matters where a loss may be reasonably possible, but not probable, or is probable but not reasonably estimable, no accrual is established, but if the matter is material, it is subject to disclosures. The Company believes that liabilities associated with any claims, while possible, are not probable, and therefore has not recorded any accrual for any claims as of December 31, 2018 . Further, while any possible range of loss cannot be reasonably estimated at this time, the Company does not believe that the outcome of any of these proceedings, individually or in the aggregate, would, if determined adversely to it, have a material adverse effect on its financial condition or business, although an adverse resolution of legal proceedings could have a material adverse effect on the Companys results of operations or cash flow in a particular quarter or year. Contingencies Certain of the Companys revenues are subject to sales and use taxes in certain jurisdictions where it conducts business in the United States. During 2018 and 2017 , the Company estimated that a sales and use tax liability of $8,643 and $8,522 , respectively, was probable related to multiple taxing jurisdictions with respect to revenues in the years ended December 31, 2018 and December 31, 2017 , and prior years. This amount is included in accrued expenses and other liabilities on the consolidated balance sheets. For the years ended December 31, 2018 and 2017 , the Company also estimated a sales and use tax receivable of $5,246 and $2,704 , respectively, related to the estimated recoverability of a portion of the liability from customers. This amount is included in prepaid expenses and other current assets on the consolidated balance sheets. Additional future information obtained from the applicable jurisdictions may affect the Companys estimate of its sales and use tax liability, but such change in the estimate cannot currently be made.