Commitments and Contingencies Operating Lease Commitments The Company leases its facilities under non-cancelable operating leases. These operating leases expire at various dates through December 2034 and generally require the payment of real estate taxes, insurance, maintenance and operating costs. The minimum aggregate future obligations under non-cancelable leases as of December 31, 2018 were as follows (in thousands): 2019 $ 54,561 2020 78,683 2021 75,991 2022 72,579 2023 70,101 Thereafter 599,339 Total $ 951,254 Rent expense for the years ended December 31, 2018, 2017 and 2016 was $63.2 million , $58.8 million and $50.3 million , respectively. The Company has entered into sublease agreements with tenants of various properties previously vacated by the Company. The amounts paid to the Company by these sublease tenants was $3.8 million , $3.6 million and $1.3 million for the years ended December 31, 2018, 2017 and 2016 , respectively. As of December 31, 2018 , the Company had outstanding letters of credit in the amount of $7.8 million , primarily related to operating leases. The letters of credit remain in effect until the Company fulfills its obligations under these leases or as such obligations expire under the terms of the letters of credit. Purchase Commitments As of December 31, 2018 , the Company had long-term commitments for bandwidth usage and co-location with various networks and ISPs, for asset purchases for network equipment and for facilities related build-out. Additionally, as of December 31, 2018 , the Company had entered into purchase orders with various vendors. The minimum future commitments as of December 31, 2018 were as follows (in thousands): Bandwidth and Co-location Commitments Purchase Order Commitments 2019 $ 138,777 $ 156,533 2020 24,420 11,132 2021 8,463 10,559 2022 5,233 468 2023 2,156  Thereafter 3,709  Total $ 182,758 $ 178,692 Legal Matters The Company is party to various litigation matters that management considers routine and incidental to its business. Management does not expect the results of any of these routine actions to have a material effect on the Companys business, results of operations, financial condition or cash flows. In July 2016, as part of the resolution of a patent infringement lawsuit filed by the Company against Limelight Networks, Inc. (Limelight) in 2006, the Company entered into an agreement that requires Limelight to pay the Company $54.0 million in 12 equal installments over three years , beginning in August 2016. During the years ended December 31, 2018, 2017 and 2016, the Company received $18.0 million , $18.0 million and $9.0 million , respectively, under this agreement. Substantially all of the amounts received were recorded as a gain contingency, which reduced general and administrative expenses in the consolidated statements of income, with the remaining as interest income. In April 2018, as part of the resolution of multiple existing lawsuits between Limelight and the Company, including in the U.S. District Court for the Eastern District of Virginia and in the U.S. District Court for the District of Massachusetts, the Company and Limelight entered into an agreement to settle the cases and request that the U.S. Patent Trial and Appeal Board terminate certain proceedings related to patents at issue in the litigation. The Company recorded a $14.9 million charge in the second quarter of 2018, which is included in general and administrative expenses in the consolidated statement of income for the year ended December 31, 2018, related to this settlement. Indemnification The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company agrees to indemnify, hold harmless and reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company's business partners, vendors or customers, in connection with its provision of its services. Generally, these obligations are limited to claims relating to infringement of a patent, copyright or other intellectual property right or the Companys negligence, willful misconduct or violation of law. Subject to applicable statutes of limitation, the term of each of these indemnification agreements is generally perpetual from the time of execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company carries insurance that covers certain third-party claims relating to its services and activities and that could limit the Companys exposure in that respect. The Company has agreed to indemnify each of its officers and directors during his or her lifetime for certain events or occurrences that happen by reason of the fact that the officer or director is or was or has agreed to serve as an officer or director of the Company. The Company has director and officer insurance policies that may limit its exposure and may enable the Company to recover a portion of certain future amounts paid. To date, the Company has not encountered material costs as a result of such indemnification obligations and has not accrued any related liabilities in its financial statements. In assessing whether to establish an accrual, the Company considers such factors as the degree of probability of an unfavorable outcome and the ability to make a reasonable estimate of the amount of loss.