Commitments and Contingencies As of December 31, 2019 , our contractual obligations are as follows for the years ending December 31 (in thousands): Operating Lease Obligations (1) Purchase Commitments (2) Convertible Senior Notes (3) Total 2020 $ 30,543 $ 91,020 $ 1,438 $ 123,001 2021 26,330 64,229 1,438 91,997 2022 24,121 56,763 1,438 82,322 2023 16,846 41,250 575,299 633,395 2024 7,456   7,456 Thereafter 24,299  24,299 Total $ 129,595 $ 253,262 $ 579,613 $ 962,470 (1) Represents obligations to make payments under non-cancellable lease agreements for our corporate headquarters and worldwide offices. (2) Primarily relates to third-party managed hosting services. (3) Consists of principal and interest payments. The $575 million in principal is due March 2023. Letters of Credit As of December 31, 2019 and 2018 , we had a total of $4 million and $1 million , respectively in unsecured letters of credit outstanding primarily related to leased office space in San Francisco. These letters of credit renew annually and mature at various dates through October 31, 2022 . Litigation and Loss Contingencies We accrue estimates for resolution of legal and other contingencies when losses are probable and estimable. These estimates are reviewed at least quarterly and adjusted to reflect the impacts of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. On October 24, 2019 and November 7, 2019, purported stockholders of the Company filed two putative class action complaints in the United States District Court for the Northern District of California, entitled Charles Reidinger v. Zendesk, Inc., et al., Case No. 3:19-cv-06968-CRB and Ho v. Zendesk, Inc., et al., No. 3:19-cv-07361-WHA, respectively, against the Company and certain of the Companys executive officers. The complaints are nearly identical and allege violations of Section 10(b) and Section 20(a) of the Securities Exchange Act of 1934, as amended, purportedly on behalf of all persons who purchased Zendesk, Inc. common stock between February 6, 2019 and October 1, 2019, inclusive. The claims are based upon allegations that the defendants misrepresented and/or omitted material information in certain of our prior public filings. To this point, no discovery has occurred in these cases. The court has appointed lead plaintiff and has consolidated the various lawsuits into a single action (Case No. 3:19-cv-06968-CRB). It is possible that additional similar complaints or additional amended complaints may be filed. If this occurs, we do not intend to announce the filing of each additional, similar complaint or any amended complaint unless it contains allegations that are substantially distinct from those made in the pending action described above. These class actions are still in the preliminary stages, and it is not possible for the Company to quantify the extent of potential liability to the individual defendants, if any. Management believes that these lawsuits lack merit and intends to vigorously defend the actions. We cannot predict the outcome of or estimate the possible loss or range of loss from the above described matters. From time to time, we may be subject to other legal proceedings, claims, investigations, and government inquiries in the ordinary course of business. We have received, and may in the future continue to receive, claims from third parties asserting, among other things, infringement of their intellectual property rights, labor and employment rights, defamation, privacy, and contractual rights. In general, the resolution of a legal matter could prevent the Company from offering its service to others, could be material to the Companys financial condition or cash flows, or both, or could otherwise adversely affect the Companys operating results. The outcomes of legal proceedings and other contingencies are inherently unpredictable and subject to significant uncertainties. As a result, the Company is not able to reasonably estimate the amount or range of possible losses in excess of any amounts accrued, including losses that could arise as a result of application of non-monetary remedies, with respect to the contingencies it faces. In managements opinion, resolution of all current matters is not expected to have a material adverse impact on business, consolidated balance sheets, results of operations, comprehensive loss, or cash flows. Indemnifications In the ordinary course of business, we enter into contractual arrangements under which we agree to provide indemnification of varying scope and terms to customers, business partners, and other parties with respect to certain matters, including, but not limited to, losses arising out of the breach of such agreements, intellectual property infringement claims made by third parties, and other liabilities relating to or arising from our product and platform solutions or our acts or omissions. In these circumstances, payment may be conditional on the other party making a claim pursuant to the procedures specified in the particular contract. Further, our obligations under these agreements may be limited in terms of time and/or amount, and in some instances, we may have recourse against third parties for certain payments. In addition, we have indemnification agreements with our directors and executive officers that require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The terms of such obligations may vary. To date, we have not incurred any material costs, and we have not accrued any liabilities in our consolidated financial statements, as a result of these obligations. Certain of our solutions include service-level agreements warranting defined levels of uptime reliability and performance, which permit those customers to receive credits for future services in the event that we fail to meet those levels. To date, we have not accrued for any material liabilities in our consolidated financial statements as a result of these service-level agreements.