Commitments and Contingencies Operating Leases The Company has commitments under non-cancelable operating leases for facilities, certain equipment, and its managed data center facilities. Total rental expenses were $12.6 million and $12.7 million for the years ended December 31, 2018 and 2017 , respectively. Additionally, expenses for cloud-based services related to data centers were $7.1 million and $4.9 million for the years ended December 31, 2018 and 2017 , respectively. As of December 31, 2018 and December 31, 2017 , the Company had $2.9 million of letters of credit associated with office leases available for borrowing, on which there were no outstanding borrowings as of either date. The following table summarizes the Company's future minimum lease payments under non-cancelable operating leases and related sublease income at December 31, 2018 : 2019 2020 2021 2022 2023 Total (in thousands) Operating lease expense $ 6,773 $ 3,880 $ 1,734 $ 1,019 $ 597 $ 14,003 Operating sublease income (285 ) (194 ) (194 ) (194 ) (145 ) (1,012 ) Total $ 6,488 $ 3,686 $ 1,540 $ 825 $ 452 $ 12,991 Guarantees and Indemnification The Companys agreements with sellers, buyers, and other third parties typically obligate it to provide indemnity and defense for losses resulting from claims of intellectual property infringement, damages to property or persons, business losses, or other liabilities. Generally, these indemnity and defense obligations relate to the Companys own business operations, obligations, and acts or omissions. However, under some circumstances, the Company agrees to indemnify and defend contract counterparties against losses resulting from their own business operations, obligations, and acts or omissions, or the business operations, obligations, and acts or omissions of third parties. For example, because the Companys business interposes the Company between buyers and sellers in various ways, buyers often require the Company to indemnify them against acts and omissions of sellers, and sellers often require the Company to indemnify them against acts and omissions of buyers. In addition, the Companys agreements with sellers, buyers, and other third parties typically include provisions limiting the Companys liability to the counterparty, and the counterpartys liability to the Company. These limits sometimes do not apply to certain liabilities, including indemnity obligations. These indemnity and limitation of liability provisions generally survive termination or expiration of the agreements in which they appear. The Company has also entered into indemnification agreements with its directors, executive officers and certain other officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. No material demands have been made upon the Company to provide indemnification under such agreements and there are no claims that the Company is aware of that could have a material effect on the Companys consolidated financial statements. Litigation The Company and its subsidiaries may from time to time be parties to legal or regulatory proceedings, lawsuits and other claims incident to their business activities and to the Companys status as a public company. Such matters may include, among other things, assertions of contract breach or intellectual property infringement, claims for indemnity arising in the course of the Companys business, regulatory investigations or enforcement proceedings, and claims by persons whose employment has been terminated. Such matters are subject to many uncertainties, and outcomes are not predictable with assurance. Consequently, management is unable to ascertain the ultimate aggregate amount of monetary liability, amounts which may be covered by insurance or recoverable from third parties, or the financial impact with respect to such matters as of December 31, 2018 . However, based on managements knowledge as of December 31, 2018 , management believes that the final resolution of these matters known at such date, individually and in the aggregate, will not have a material adverse effect upon the Companys consolidated financial position, results of operations or cash flows. On March 31, 2017, Guardian News &amp; Media Limited ("Guardian") issued proceedings (the "Complaint") against the Company in the Chancery Division of the High Court of Justice in England &amp; Wales. The Complaint alleged that the Company underpaid Guardian for digital advertising inventory sold by Guardian through the Company's platform as a result of the fact that the Company charged fees to buyers of that inventory. Guardian claimed the Company was precluded from charging buyer fees as a result of the contractual arrangements with Guardian and English agency law principles, as well as representations it allegedly made to Guardian. The Complaint claimed damages including loss of revenue, interest, and costs. On October 11, 2018, the Company and Guardian mutually agreed to resolve their dispute and the High Court proceedings have been discontinued. Though the terms of the settlement agreement are confidential, the settlement is immaterial to the Company from a financial standpoint. Employment Contracts The Company has entered into severance agreements with certain employees and officers. The Company may be required to pay severance and accelerate the vesting of certain equity awards in the event of involuntary terminations.