Commitments and Contingencies	3 Months Ended
Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Commitments The Company’s principal commitments consist of future payment obligations under capital leases to finance data centers and other computer and networking equipment purchases, operating lease agreements for office space, research and development, and sales and marketing facilities, and agreements with third parties to provide co-location hosting, telecommunication usage and equipment maintenance services. These commitments as of December 31, 2015 are disclosed in the Company's Annual Report on Form 10-K for the year ended December 31, 2015, and did not change materially during the three months ended March 31, 2016 except for the acquisition of certain additional data center and network equipment and software under multiple capital leases. As of March 31, 2016, the total minimum future payment commitments under these capital leases added during the three months ended March 31, 2016 were approximately $1.7 million, of which $0.5 million is due in 2016, with the remainder due over approximately 28 months. Universal Services Fund Liability During the third quarter of 2012, the Company determined that based on its business activities, it is classified as a telecommunications service provider for regulatory purposes and it should make direct contributions to the federal USF and related funds based on revenues it receives from the resale of interstate and international telecommunications services. Previously, the Company had believed that the telecommunications services were an integral part of an information service that the Company provides via its software and had instead made indirect USF contributions via payments to its wholesale telecommunications service providers. In order to comply with the obligation to make direct contributions, the Company made a voluntary self-disclosure to the FCC Enforcement Bureau and registered with the USAC, which is charged by the FCC with administering the USF. The Company filed exemption certificates with its wholesale telecommunications service providers in order to eliminate its obligation to reimburse such wholesale telecommunications service providers for their USF contributions calculated on services sold to the Company. The Company’s registration with USAC subjects it to assessments for unpaid USF contributions, as well as interest thereon and civil penalties, due to its late registration and past failure to recognize its obligation as a USF contributor and as an international carrier. The Company will be required to pay assessments for periods prior to the Company’s registration. As of December 31, 2012, the total past due USF contribution being imposed by USAC and accrued by the Company for the period from 2003 through 2012 was $8.1 million, of which $4.7 million was undisputed and $3.4 million, including $0.8 million that pertains to 2003 through 2007, was disputed. While the Company is in administrative proceedings before the FCC to limit such back assessments to the period 2008 through 2012, it is possible that it will be required to pay back assessments for the period from 2003 through 2007. In 2013, the Company began remitting required contributions on a prospective basis directly to USAC. In July 2013, the Company and USAC agreed to a financing arrangement for $4.1 million of the undisputed $4.7 million of the unpaid USF contributions whereby the Company issued to USAC a promissory note payable in the principal amount of the $4.1 million and paid off the remaining undisputed $0.6 million. The repayment terms of the promissory note payable are disclosed in Note 5. As of March 31, 2016 and December 31, 2015, the principal balance of the promissory note payable was $1.1 million and $1.5 million, respectively, and is included in the notes payable amounts on the condensed consolidated balance sheets. In addition to the promissory note payable, as of March 31, 2016 and December 31, 2015, the Company had an accrued liability for the disputed portion of the unpaid USF contributions and estimated interest and penalties of $4.9 million included in accrued federal fees on the condensed consolidated balance sheets. For each of the three months ended March 31, 2016 and 2015, the Company recorded interest and penalty expenses of $0.1 million as a charge to general and administrative expense, which were related to its disputed unpaid USF obligations. On June 12, 2015, in connection with the Company’s disclosure to the FCC, the Company entered into a consent decree with the FCC Enforcement Bureau. In the consent decree, the Company agreed to pay a civil penalty of $2.0 million to the U.S. Treasury in twelve equal quarterly installments starting in July 2015 without interest (Note 5). In the third quarter of 2014, the Company accrued a $2.0 million liability for the then tentative civil penalty. The consent decree also requires the Company to adopt certain internal regulatory compliance monitoring and training requirements, and to report on the status of those compliance efforts to the FCC’s Enforcement Bureau for three years. The Company’s implementation of the internal regulatory compliance monitoring and training requirements were completed in August 2015, and its annual compliance reporting to the FCC will continue until June 2018. State and Local Taxes and Surcharges In April 2012, the Company commenced collecting and remitting sales taxes on sales of subscription services in all the U.S. states in which it determined it was obligated to do so. During the first quarter of 2015, the Company conducted an updated sales tax review of the taxability of sales of its subscription services. As a result, the Company determined that it may be obligated to collect and remit sales taxes on such sales in four additional states. Based on its best estimate of the probable sales tax liability in those four states relating to its sales of subscription services during the period 2011 through 2014, during the three months ended March 31, 2015, the Company recorded a general and administrative expense of $0.6 million as an immaterial out of period adjustment to accrue for such taxes. During 2013, the Company analyzed its activities and determined it may be obligated to collect and remit various state and local taxes and surcharges on its usage-based fees. The Company had not remitted state and local taxes on usage-based fees in any of the periods prior to 2014 and therefore accrued a sales tax liability for this contingency. In January 2014, the Company commenced paying such taxes and surcharges to certain state authorities. In June 2014, the Company commenced collecting state and local taxes or surcharges on usage-based fees from its clients on a current basis and remitting such taxes to the applicable U.S. state taxing authorities. During the three months ended March 31, 2016 and 2015, respectively, the Company remitted $0.2 million and $27 thousand for its contingent sales taxes on both usage-based fees and sales of subscription services. For the three months ended March 31, 2016 and 2015, the Company recognized $6 thousand and $0.7 million, respectively, as general and administrative expense related to its estimated sales tax liability on both usage-based fees and sales of subscription services in the U.S. and Canada, which was not being collected from its clients. As of March 31, 2016 and December 31, 2015, the Company had total accrued liabilities of $2.5 million and $2.7 million, respectively, for such contingent sales taxes and surcharges that were not being collected from its clients but may be imposed by various taxing authorities, of which $0.6 million and $0.8 million were included in current “Sales tax liability” on the condensed consolidated balance sheets, respectively, and the remaining were included in non-current “Sales tax liability” on the condensed consolidated balance sheets. The Company’s estimate of the probable loss incurred under this contingency is based on its analysis of the source location of its usage-based fees and the regulations and rules in each tax jurisdiction. Legal Matters The Company is involved in various legal and regulatory matters arising in the normal course of business. In management’s opinion, resolution of these matters is not expected to have a material impact on the Company’s consolidated results of operations, cash flows, or its financial position. However, due to the uncertain nature of legal matters, an unfavorable resolution of a matter could materially affect the Company’s future consolidated results of operations, cash flows or financial position in a particular period. The Company is currently involved in the following lawsuit as a defendant. NobelBiz Litigation On August 5, 2011, NobelBiz sent a letter to the Company asserting infringement of a patent related to virtual call centers. On April 3, 2012, NobelBiz filed a patent infringement lawsuit against the Company in the United States District Court for the Eastern District of Texas. The patent asserted in the complaint is different, but related, to the patent asserted in the original letter. The lawsuit, NobelBiz Inc. v. Five9, Inc., Case No. 6:12-cv-00243-LED, alleges that the Company’s local caller ID management service infringes United States Patent No. 8,135,122, or the ‘122 patent. The ‘122 patent, titled “System and Method for Modifying Communication Information (MCI),” issued on March 13, 2012, and according to the complaint is alleged to relate to “a system for processing a telephone call from a call originator (also referred to as a calling party) to a call target (also referred to as a receiving party), where the system accesses a database storing outgoing telephone numbers, selects a replacement telephone number from the outgoing telephone numbers based on the telephone number of the call target, and originates an outbound call to the call target with a modified outgoing caller identification (‘caller ID’).” NobelBiz seeks damages in the form of lost profits as well as injunctive relief. The lawsuit is one of several lawsuits filed by NobelBiz against various companies including TCN Inc., LiveVox, Inc. and Global Connect LLC. On March 28, 2013, the court granted the Company’s motion to transfer the case to the United States District Court for the Northern District of California. Subsequently, NobelBiz amended its complaint to add claims related to U.S. Patent No. 8,565,399, or the ‘399 patent, which is a continuation in the same family as the ‘122 patent and addresses the same technology. The Company responded to the complaint and amended complaint by asserting noninfringement and invalidity of the ‘122 and ‘399 patents. On January 16, 2015, the court issued an order regarding claim construction of the two patents-in-suit. On March 7, 2016, the court stayed the case pending an appeal in lawsuits involving NobelBiz, Global Connect and TCN that also involve the ‘122 and ‘399 patents. The appeal for those cases is likely to last until later this year or next year, after which time the lawsuit between NobelBiz and Five9 will resume and a new schedule will be entered by the Court. The Company has investigated the claims alleged in the complaint and believes that it has good defenses to the claims. While the Company does not believe that it is probable that a loss has been incurred, the ultimate resolution of the matter could potentially result in a loss. Management’s best estimate of the low end of the range of the potential loss is zero. At this time, it is not possible to reasonably estimate the high end of the range of the potential loss, which could be material to the Company’s results of operations. Accordingly, the Company has not accrued a loss related to this matter. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to clients, vendors, lessors, business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements, services to be provided by the Company or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its directors, officers and certain employees that 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 demands have been made upon the Company to provide indemnification under such agreements and thus there are no claims that the Company is aware of that would have a material effect on the Company’s condensed consolidated balance sheets, condensed consolidated statements of operations and comprehensive loss, or condensed consolidated statements of cash flows.

9. Commitments and Contingencies

Commitments

The Company’s principal commitments consist of future payment obligations under capital leases to finance data centers and other computer and networking equipment purchases, operating lease agreements for office space, research and development, and sales and marketing facilities, and agreements with third parties to provide co-location hosting, telecommunication usage and equipment maintenance services. These commitments as of December 31, 2015 are disclosed in the Company's Annual Report on Form 10-K for the year ended December 31, 2015, and did not change materially during the three months ended March 31, 2016 except for the acquisition of certain additional data center and network equipment and software under multiple capital leases. As of March 31, 2016, the total minimum future payment commitments under these capital leases added during the three months ended March 31, 2016 were approximately $1.7 million, of which $0.5 million is due in 2016, with the remainder due over approximately 28 months.

Universal Services Fund Liability

During the third quarter of 2012, the Company determined that based on its business activities, it is classified as a telecommunications service provider for regulatory purposes and it should make direct contributions to the federal USF and related funds based on revenues it receives from the resale of interstate and international telecommunications services. Previously, the Company had believed that the telecommunications services were an integral part of an information service that the Company provides via its software and had instead made indirect USF contributions via payments to its wholesale telecommunications service providers. In order to comply with the obligation to make direct contributions, the Company made a voluntary self-disclosure to the FCC Enforcement Bureau and registered with the USAC, which is charged by the FCC with administering the USF. The Company filed exemption certificates with its wholesale telecommunications service providers in order to eliminate its obligation to reimburse such wholesale telecommunications service providers for their USF contributions calculated on services sold to the Company.

The Company’s registration with USAC subjects it to assessments for unpaid USF contributions, as well as interest thereon and civil penalties, due to its late registration and past failure to recognize its obligation as a USF contributor and as an international carrier. The Company will be required to pay assessments for periods prior to the Company’s registration. As of December 31, 2012, the total past due USF contribution being imposed by USAC and accrued by the Company for the period from 2003 through 2012 was $8.1 million, of which $4.7 million was undisputed and $3.4 million, including $0.8 million that pertains to 2003 through 2007, was disputed. While the Company is in administrative proceedings before the FCC to limit such back assessments to the period 2008 through 2012, it is possible that it will be required to pay back assessments for the period from 2003 through 2007. In 2013, the Company began remitting required contributions on a prospective basis directly to USAC.

In July 2013, the Company and USAC agreed to a financing arrangement for $4.1 million of the undisputed $4.7 million of the unpaid USF contributions whereby the Company issued to USAC a promissory note payable in the principal amount of the $4.1 million and paid off the remaining undisputed $0.6 million. The repayment terms of the promissory note payable are disclosed in Note 5. As of March 31, 2016 and December 31, 2015, the principal balance of the promissory note payable was $1.1 million and $1.5 million, respectively, and is included in the notes payable amounts on the condensed consolidated balance sheets. In addition to the promissory note payable, as of March 31, 2016 and December 31, 2015, the Company had an accrued liability for the disputed portion of the unpaid USF contributions and estimated interest and penalties of $4.9 million included in accrued federal fees on the condensed consolidated balance sheets. For each of the three months ended March 31, 2016 and 2015, the Company recorded interest and penalty expenses of $0.1 million as a charge to general and administrative expense, which were related to its disputed unpaid USF obligations.

On June 12, 2015, in connection with the Company’s disclosure to the FCC, the Company entered into a consent decree with the FCC Enforcement Bureau. In the consent decree, the Company agreed to pay a civil penalty of $2.0 million to the U.S. Treasury in twelve equal quarterly installments starting in July 2015 without interest (Note 5). In the third quarter of 2014, the Company accrued a $2.0 million liability for the then tentative civil penalty. The consent decree also requires the Company to adopt certain internal regulatory compliance monitoring and training requirements, and to report on the status of those compliance efforts to the FCC’s Enforcement Bureau for three years. The Company’s implementation of the internal regulatory compliance monitoring and training requirements were completed in August 2015, and its annual compliance reporting to the FCC will continue until June 2018.

State and Local Taxes and Surcharges

In April 2012, the Company commenced collecting and remitting sales taxes on sales of subscription services in all the U.S. states in which it determined it was obligated to do so. During the first quarter of 2015, the Company conducted an updated sales tax review of the taxability of sales of its subscription services. As a result, the Company determined that it may be obligated to collect and remit sales taxes on such sales in four additional states. Based on its best estimate of the probable sales tax liability in those four states relating to its sales of subscription services during the period 2011 through 2014, during the three months ended March 31, 2015, the Company recorded a general and administrative expense of $0.6 million as an immaterial out of period adjustment to accrue for such taxes.

During 2013, the Company analyzed its activities and determined it may be obligated to collect and remit various state and local taxes and surcharges on its usage-based fees. The Company had not remitted state and local taxes on usage-based fees in any of the periods prior to 2014 and therefore accrued a sales tax liability for this contingency. In January 2014, the Company commenced paying such taxes and surcharges to certain state authorities. In June 2014, the Company commenced collecting state and local taxes or surcharges on usage-based fees from its clients on a current basis and remitting such taxes to the applicable U.S. state taxing authorities.

During the three months ended March 31, 2016 and 2015, respectively, the Company remitted $0.2 million and $27 thousand for its contingent sales taxes on both usage-based fees and sales of subscription services. For the three months ended March 31, 2016 and 2015, the Company recognized $6 thousand and $0.7 million, respectively, as general and administrative expense related to its estimated sales tax liability on both usage-based fees and sales of subscription services in the U.S. and Canada, which was not being collected from its clients.

As of March 31, 2016 and December 31, 2015, the Company had total accrued liabilities of $2.5 million and $2.7 million, respectively, for such contingent sales taxes and surcharges that were not being collected from its clients but may be imposed by various taxing authorities, of which $0.6 million and $0.8 million were included in current “Sales tax liability” on the condensed consolidated balance sheets, respectively, and the remaining were included in non-current “Sales tax liability” on the condensed consolidated balance sheets. The Company’s estimate of the probable loss incurred under this contingency is based on its analysis of the source location of its usage-based fees and the regulations and rules in each tax jurisdiction.

Legal Matters

The Company is involved in various legal and regulatory matters arising in the normal course of business. In management’s opinion, resolution of these matters is not expected to have a material impact on the Company’s consolidated results of operations, cash flows, or its financial position. However, due to the uncertain nature of legal matters, an unfavorable resolution of a matter could materially affect the Company’s future consolidated results of operations, cash flows or financial position in a particular period.

The Company is currently involved in the following lawsuit as a defendant.

NobelBiz Litigation

On August 5, 2011, NobelBiz sent a letter to the Company asserting infringement of a patent related to virtual call centers. On April 3, 2012, NobelBiz filed a patent infringement lawsuit against the Company in the United States District Court for the Eastern District of Texas. The patent asserted in the complaint is different, but related, to the patent asserted in the original letter. The lawsuit, NobelBiz Inc. v. Five9, Inc., Case No. 6:12-cv-00243-LED, alleges that the Company’s local caller ID management service infringes United States Patent No. 8,135,122, or the ‘122 patent. The ‘122 patent, titled “System and Method for Modifying Communication Information (MCI),” issued on March 13, 2012, and according to the complaint is alleged to relate to “a system for processing a telephone call from a call originator (also referred to as a calling party) to a call target (also referred to as a receiving party), where the system accesses a database storing outgoing telephone numbers, selects a replacement telephone number from the outgoing telephone numbers based on the telephone number of the call target, and originates an outbound call to the call target with a modified outgoing caller identification (‘caller ID’).” NobelBiz seeks damages in the form of lost profits as well as injunctive relief. The lawsuit is one of several lawsuits filed by NobelBiz against various companies including TCN Inc., LiveVox, Inc. and Global Connect LLC. On March 28, 2013, the court granted the Company’s motion to transfer the case to the United States District Court for the Northern District of California. Subsequently, NobelBiz amended its complaint to add claims related to U.S. Patent No. 8,565,399, or the ‘399 patent, which is a continuation in the same family as the ‘122 patent and addresses the same technology. The Company responded to the complaint and amended complaint by asserting noninfringement and invalidity of the ‘122 and ‘399 patents. On January 16, 2015, the court issued an order regarding claim construction of the two patents-in-suit. On March 7, 2016, the court stayed the case pending an appeal in lawsuits involving NobelBiz, Global Connect and TCN that also involve the ‘122 and ‘399 patents. The appeal for those cases is likely to last until later this year or next year, after which time the lawsuit between NobelBiz and Five9 will resume and a new schedule will be entered by the Court.

The Company has investigated the claims alleged in the complaint and believes that it has good defenses to the claims. While the Company does not believe that it is probable that a loss has been incurred, the ultimate resolution of the matter could potentially result in a loss. Management’s best estimate of the low end of the range of the potential loss is zero. At this time, it is not possible to reasonably estimate the high end of the range of the potential loss, which could be material to the Company’s results of operations. Accordingly, the Company has not accrued a loss related to this matter.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to clients, vendors, lessors, business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements, services to be provided by the Company or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its directors, officers and certain employees that 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 demands have been made upon the Company to provide indemnification under such agreements and thus there are no claims that the Company is aware of that would have a material effect on the Company’s condensed consolidated balance sheets, condensed consolidated statements of operations and comprehensive loss, or condensed consolidated statements of cash flows.