Commitments and contingencies Lease commitments In May 2016, the Company entered into a lease amendment (the "2016 Lease") for office and laboratory space currently occupied under an original lease that commenced in March 2014 and was set to expire in February 2017 (the "2014 Lease"). The 2016 Lease extended the 2014 Lease by three years through February 2020. In June 2015, the Company signed a second operating lease (the "2015 Lease") for office space in the same building as the 2014 Lease. In August 2016, the Company exercised a three -year renewal option extending the 2015 Lease to February 2020. The combined minimum future lease payments under both the 2016 Lease and the 2015 Lease are as follows (in thousands): June 30, 2017 2017 $ 791 2018 1,607 2019 1,637 2020 274 Total $ 4,309 At June 30, 2017 and December 31, 2016 , the Company has an outstanding letter of credit of $316 thousand with a financial institution related to a security deposit for the 2016 Lease, which is secured by cash on deposit and expires on February 29, 2020. An additional unsecured deposit was required for the 2015 Lease. Significant Contracts and Agreements In addition to lease commitments, the Company enters into contractual arrangements that obligate it to make payments to the contractual counterparties upon the occurrence of future events. In the normal course of operations, the Company enters into license and other agreements and intends to continue to seek additional rights related to compounds or technologies in connection with its discovery, manufacturing and development programs. These agreements may require payments to be made by the Company upon the occurrence of certain development milestones and certain commercialization milestones for each distinct product covered by the licensed patents (in addition to certain royalties to be paid on marketed products or sublicense income) contingent upon the occurrence of future events that cannot be reasonably estimated. In September 2014, the Company received $1.2 million in the form o