COMMITMENTS Leases Headquarters Lease In May 2017, we entered into a Lease Agreement (the Lease) for our corporate headquarters located in Alameda, California (the Initial Premises). The Lease was subsequently amended in October 2017, June 2018, April 2019 and August 2019, resulting in, among other things, an increase to the amount of space leased and changes to the lease term. Our right-of-use asset, lease liability and the related lease costs reflect the 221,464 square feet of space we have taken possession of as of December 31, 2019 (the Current Premises) under the amended Lease. We expect to take possession of the remainder of the space provided for under the August 2019 amendment on or prior to April 30, 2020, which will increase the space leased to 228,941 square feet. The term of the Lease continues through October 31, 2031 (the Lease Term). We have two five-year options to extend the Lease; these optional periods have not been considered in the determination of the right-of-use asset or the lease liability for the Lease as we did not consider it reasonably certain that we would exercise any such options. We have made certain tenant improvements on the Initial Premises, for which we received $8.2 million in reimbursements in January 2019. We were also provided an allowance of up to $1.7 million for tenant improvements to the space we obtained under the April 2019 amendment which is expected to be received in 2020. The balance sheet classification of our operating lease assets and liabilities were as follows (in thousands): December 31, 2019 2018 Assets: Right-of-use assets included in other long-term assets $ 41,835 $ 5,867 Liabilities: Current portion included in other current liabilities $ 2,728 $ 2,738 Long-term portion of operating lease liabilities 48,011 12,099 Total operating lease liabilities $ 50,739 $ 14,837 The components of operating lease costs, which are included in selling, general and administrative expenses in our Consolidated Statements of Income, were as follows (in thousands): Year Ended December 31, 2019 2018 2017 (1) Operating lease cost $ 2,844 $ 4,189 $ 3,944 Variable lease cost 1,024 1,661 2,216 Sublease income   (1,225 ) Total operating lease costs $ 3,868 $ 5,850 $ 4,935 ____________________ (1) The 2017 amounts have not been adjusted for the adoption of Topic 842 and continue to be reported in accordance with the previous lease guidance, ASC Topic 840: Leases . Cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2019 was $2.9 million and was included in net cash provided by operating activities in our Consolidated Statements of Cash Flows. As of December 31, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Year Ending December 31, Amount 2020 $ 4,538 2021 4,669 2022 4,820 2023 5,147 2024 5,407 Thereafter 41,585 Total lease payments 66,166 Less: Imputed interest (13,685 ) Future tenant improvement reimbursements (1,742 ) Operating lease liabilities $ 50,739 As of December 31, 2019 , the weighted average discount rate used to determine the operating lease liability was 3.9% and the weighted average remaining lease term is 11.8 years . Build-to-Suit Lease In October 2019, we entered into a build-to-suit Lease Agreement (the Build-to-Suit Lease) for approximately 220,000 square feet of office space located in Alameda, California (the New Premises), adjacent to the Current Premises. The term of the Build-to-Suit Lease is for a period of 242 months (the Term), which will begin upon the substantial completion of the building and tenant improvements by the lessor. We currently anticipate that the Term will begin in October 2021 (the Lease Commencement Date). The monthly base rent under the Build-to-Suit Lease will equal a percentage of the total development costs incurred in connection with the development of the New Premises (excluding the cost of the tenant improvements in excess of the allowance provided by the lessor and any development costs we pay) and is currently estimated to be about $0.7 million , subject to an annual increase of 3% during the Term. We will also be responsible for paying operating expenses related to the New Premises. The rent payments will begin sixty days following commencement of the Term. We have been provided a tenant improvement allowance for the New Premises of approximately $16.5 million . To the extent that the total development costs of the New Premises exceeds $525 per square foot, we will also pay 50% of such excess costs prior to the commencement of the Term, and may be required to secure such amount and the cost of the tenant improvements in excess of the allowance by providing a letter of credit or depositing such amounts in an account with the lessors lender prior to the start of construction. The Build-to-Suit Lease includes two five-year options to extend the term of the Build-to-Suit Lease, exercisable under certain conditions and at a market rate determined in accordance with the Build-to-Suit Lease. We have a one-time option to terminate the Build-to-Suit Lease without cause after the 180 th month of the Term, exercisable under certain conditions as described in the Build-to-Suit Lease and subject to a termination payment calculated in accordance with the Build-to-Suit Lease. In addition, we have a right of first offer to purchase the New Premises, subject to certain procedures and exclusions set forth in the Build-to-Suit Lease. We have determined that, under the guidance provided in Topic 842, we do not have control of the New Premises during the construction period . Therefore, we will not record a right-of-use asset or lease liability for the Build-to-Suit Lease until the Lease Commencement Date . We will evaluate the classification the Build-to-Suit Lease as an operating lease or financing lease at the Lease Commencement Date. Letters of Credit We have obtained standby letters of credit related to our lease obligations and certain other obligations with combined credit limits of $1.6 million and $1.1 million as of December 31, 2019 and 2018 , respectively. None of our letters of credit have been drawn upon. All of the letters of credit are fully collateralized by certificates of deposit.