Description of Business and Summary of Significant Accounting Policies	6 Months Ended
Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Summary of Significant Accounting Policies	Description of Business and Summary of Significant Accounting Policies Five9, Inc. and its wholly-owned subsidiaries (the “Company”) is a provider of cloud software for contact centers. The Company was incorporated in Delaware in 2001 and is headquartered in San Ramon, California. The Company has offices in Europe and Asia, which primarily provide research, development, sales, marketing, and client support services. Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. All intercompany transactions and balances have been eliminated in consolidation. Certain prior period amounts included in the condensed consolidated financial statements have been reclassified to conform to the current period presentation. Use of Estimates The preparation of condensed consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. The significant estimates made by management affect revenue, the allowance for doubtful accounts, loss contingencies, including the Company’s accrual for federal fees and sales tax liability, and accrued liabilities. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation. Actual results could differ from those estimates. Cash and Cash Equivalents The Company’s cash and cash equivalents consist of highly liquid investments with maturities of three months or less at the time of purchase. The Company’s cash equivalents consist of investments in U.S. agency securities, commercial paper, certificates of deposit and money market funds. Marketable Investments The Company’s marketable investments consist of U.S agency securities and government sponsored securities, U.S. treasury securities, certificates of deposit, corporate bonds and commercial paper. The Company determines the appropriate classification of its investments in marketable investments at the time of purchase and re-evaluates such designation at each balance sheet date. The Company’s marketable investments have been classified and accounted for as available-for-sale. Marketable investments are carried at fair value. Significant Accounting Policies The Company’s significant accounting policies are disclosed in its Annual Report on Form 10-K for the year ended December 31, 2017. Other than the accounting policies discussed in Note 2 related to the adoption of ASC 606, there has been no material change to the Company’s significant accounting policies during the six months ended June 30, 2018. See Note 2 for the updated accounting policies. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers: Topic 606, amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ASU 2014-09 also includes Subtopic 340-40, Other Assets and Deferred Costs - Contracts with Customers, which requires the deferral of incremental costs of obtaining a contract with a customer. The Company adopted ASU 2014-09 and its related amendments (collectively “ASC 606”) effective on January 1, 2018 using the modified retrospective method. See Note 2 for disclosure on the impact of adopting this standard. Recent Accounting Pronouncements Not Yet Effective In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Under the new guidance, a lessee will be required to recognize assets and liabilities for both finance, or capital, and operating leases with lease terms of more than 12 months. The ASU also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting will remain largely unchanged from current GAAP. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that includes a number of optional practical expedients that entities may elect to apply. This guidance is effective for the Company beginning in the first quarter of 2019. Early adoption is permitted. The Company is currently gathering information and evaluating the impact this guidance will have on its consolidated financial statements. There are several other new accounting pronouncements issued by the FASB, which the Company will adopt. However, the Company does not believe any of those accounting pronouncements will have a material impact on its consolidated financial position, operating results or statements of cash flows.

Description of Business and Summary of Significant Accounting Policies

Five9, Inc. and its wholly-owned subsidiaries (the “Company”) is a provider of cloud software for contact centers. The Company was incorporated in Delaware in 2001 and is headquartered in San Ramon, California. The Company has offices in Europe and Asia, which primarily provide research, development, sales, marketing, and client support services.

Basis of Presentation

The accompanying condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Therefore, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. All intercompany transactions and balances have been eliminated in consolidation.

Certain prior period amounts included in the condensed consolidated financial statements have been reclassified to conform to the current period presentation.

Use of Estimates

The preparation of condensed consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. The significant estimates made by management affect revenue, the allowance for doubtful accounts, loss contingencies, including the Company’s accrual for federal fees and sales tax liability, and accrued liabilities. Management periodically evaluates such estimates and they are adjusted prospectively based upon such periodic evaluation. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company’s cash and cash equivalents consist of highly liquid investments with maturities of three months or less at the time of purchase. The Company’s cash equivalents consist of investments in U.S. agency securities, commercial paper, certificates of deposit and money market funds.

Marketable Investments

The Company’s marketable investments consist of U.S agency securities and government sponsored securities, U.S. treasury securities, certificates of deposit, corporate bonds and commercial paper. The Company determines the appropriate classification of its investments in marketable investments at the time of purchase and re-evaluates such designation at each balance sheet date. The Company’s marketable investments have been classified and accounted for as available-for-sale. Marketable investments are carried at fair value.

Significant Accounting Policies

The Company’s significant accounting policies are disclosed in its Annual Report on Form 10-K for the year ended December 31, 2017. Other than the accounting policies discussed in Note 2 related to the adoption of ASC 606, there has been no material change to the Company’s significant accounting policies during the six months ended June 30, 2018. See Note 2 for the updated accounting policies.

Recently Adopted Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers: Topic 606, amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ASU 2014-09 also includes Subtopic 340-40, Other Assets and Deferred Costs - Contracts with Customers, which requires the deferral of incremental costs of obtaining a contract with a customer. The Company adopted ASU 2014-09 and its related amendments (collectively “ASC 606”) effective on January 1, 2018 using the modified retrospective method. See Note 2 for disclosure on the impact of adopting this standard.

Recent Accounting Pronouncements Not Yet Effective

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Under the new guidance, a lessee will be required to recognize assets and liabilities for both finance, or capital, and operating leases with lease terms of more than 12 months. The ASU also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. Lessor accounting will remain largely unchanged from current GAAP. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach that includes a number of optional practical expedients that entities may elect to apply. This guidance is effective for the Company beginning in the first quarter of 2019. Early adoption is permitted. The Company is currently gathering information and evaluating the impact this guidance will have on its consolidated financial statements.

There are several other new accounting pronouncements issued by the FASB, which the Company will adopt. However, the Company does not believe any of those accounting pronouncements will have a material impact on its consolidated financial position, operating results or statements of cash flows.