Business Overview and Basis of Presentation	12 Months Ended
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business Overview and Basis of Presentation	Business Overview and Basis of Presentation Description of Business Fitbit, Inc. (the “Company”) is a technology company focused on driving health solutions and positively impacting health outcomes. The Fitbit platform combines wearable devices with software and services to give its users tools to help them reach their health and fitness goals. The Company’s wearable devices, which include trackers and smartwatches, enable its users to view data about their daily activity, exercise and sleep in real-time. The Company’s software and services, which include an online dashboard and mobile app, provide its users with data analytics, motivational and social tools, and virtual coaching through customized fitness plans and interactive workouts, drive engagement and can be leveraged to provide personalized insights. The Company sells devices through diversified sales channels that include distributors, retailers, Fitbit Health Solutions, and Fitbit.com. The Company has established wholly-owned subsidiaries globally and its corporate headquarters are located in San Francisco, California. Basis of Presentation and Principles of Consolidation The consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated. The Company’s fiscal year ends on December 31 of each year. The Company operates on a 4-4-5 week quarterly calendar. Use of Estimates The preparation of consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the consolidated financial statements and accompanying notes. The primary estimates and assumptions made by management are related to revenue recognition, reserves for sales returns and incentives, reserves for warranty, valuation of stock-based awards, fair value of derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, fair value of goodwill and acquired tangible and intangible assets and liabilities assumed during acquisitions, the number of reportable segments, the recoverability of intangible assets and their useful lives, contingencies, income taxes, recoverability of unused advertising credits, and impairment of an equity investment. Actual results could differ from those estimates, and such differences may be material to the consolidated financial statements. Comprehensive Loss Comprehensive loss consists of two components, net loss and other comprehensive loss, net of tax. Other comprehensive loss refers to revenue, expenses, and gains and losses that are recorded as an element of stockholders’ equity but are excluded from net loss. The Company’s other comprehensive loss consists of net unrealized gains and losses on derivative instruments accounted for as cash flow hedges, foreign currency translation adjustments from those subsidiaries not using the U.S. dollar as their functional currency, and unrealized gains and losses on available-for-sale securities. Customer Bankruptcy In September 2017, Wynit Distribution (“Wynit”) filed for bankruptcy protection under Chapter 11 of the United States Bankruptcy Code. Wynit was the Company’s largest customer, historically representing 11% of total revenue during the six months ended July 1, 2017 and 19% of total accounts receivables as of July 1, 2017. In connection with Wynit’s bankruptcy filing, the Company believed that the collectability of the product shipments to Wynit during the third quarter of 2017 was not reasonably assured. However, as of July 1, 2017, collectability of accounts receivables from Wynit was reasonably assured. The Company ceased to recognize revenue from Wynit, which totaled $8.1 million during the third quarter of 2017. Additionally, the Company recorded a charge of $35.8 million during the third quarter ended September 30, 2017 comprised of cost of revenue of $5.5 million associated with shipments to Wynit in the third quarter of 2017 and bad debt expense of $30.3 million associated with all of Wynit’s outstanding accounts receivables. The Company maintains credit insurance that covers a portion of the exposure related to its customer receivables. The Company recorded an insurance receivable based on an analysis of its insurance policies, including their exclusions, an assessment of the nature of the claim, and information from its insurance carrier. As of September 30, 2017, the Company had recorded an insurance receivable of $26.8 million, included in prepaid expenses and other current assets, associated with the amount it had concluded was probable related to the claim. The $26.8 million insurance receivable allowed the Company to recover $22.7 million of bad debt expense and $4.1 million of cost of revenue, resulting in a net charge of $9.0 million in the consolidated statement of operations comprised of net bad debt expense of $7.6 million and net cost of revenue of $1.4 million. The Company received $21.4 million of the insurance receivable during the fourth quarter of 2017, and the remaining $5.4 million in January 2018. During 2018, the Company released $12.4 million in product return and rebate reserves related to Wynit, as it believes the possibility of future claims associated with these reserves is remote. This reserve release resulted in a $12.4 million increase in revenue during the year ended December 31, 2018. Non-Monetary Transaction The Company entered into an agreement with a third party during 2016 to exchange inventory for advertising credits and cash, which was amended in October 2018 to extend the contractual period from four to six years. The Company recorded the transaction based on the estimated fair value of the products exchanged. For the year ended December 31, 2016, the Company recorded $15.0 million of revenue and $7.0 million of associated cost of goods sold upon exchange of the products for advertising credits of $13.0 million and cash of $2.0 million. The $13.0 million of unused advertising credits remaining as of December 31, 2016 were recorded in prepaid expenses and other current assets, and other assets. Such credits are expected to be used over the contractual period of six years, and will be expensed as advertising services are received. During the year ended December 31, 2018 and 2017, $2.3 million and $0.8 million, respectively, of credits were utilized. The Company’s prepaid and other assets related to unused advertising credits as of December 31, 2018 and December 31, 2017 were $9.9 million and $12.2 million, respectively.

Business Overview and Basis of Presentation

Description of Business

Fitbit, Inc. (the “Company”) is a technology company focused on driving health solutions and positively impacting health outcomes. The Fitbit platform combines wearable devices with software and services to give its users tools to help them reach their health and fitness goals. The Company’s wearable devices, which include trackers and smartwatches, enable its users to view data about their daily activity, exercise and sleep in real-time. The Company’s software and services, which include an online dashboard and mobile app, provide its users with data analytics, motivational and social tools, and virtual coaching through customized fitness plans and interactive workouts, drive engagement and can be leveraged to provide personalized insights. The Company sells devices through diversified sales channels that include distributors, retailers, Fitbit Health Solutions, and Fitbit.com. The Company has established wholly-owned subsidiaries globally and its corporate headquarters are located in San Francisco, California.

Basis of Presentation and Principles of Consolidation

The consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated.

The Company’s fiscal year ends on December 31 of each year. The Company operates on a 4-4-5 week quarterly calendar.

Use of Estimates

The preparation of consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the consolidated financial statements and accompanying notes. The primary estimates and assumptions made by management are related to revenue recognition, reserves for sales returns and incentives, reserves for warranty, valuation of stock-based awards, fair value of derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, fair value of goodwill and acquired tangible and intangible assets and liabilities assumed during acquisitions, the number of reportable segments, the recoverability of intangible assets and their useful lives, contingencies, income taxes, recoverability of unused advertising credits, and impairment of an equity investment. Actual results could differ from those estimates, and such differences may be material to the consolidated financial statements.

Comprehensive Loss

Comprehensive loss consists of two components, net loss and other comprehensive loss, net of tax. Other comprehensive loss refers to revenue, expenses, and gains and losses that are recorded as an element of stockholders’ equity but are excluded from net loss. The Company’s other comprehensive loss consists of net unrealized gains and losses on derivative instruments accounted for as cash flow hedges, foreign currency translation adjustments from those subsidiaries not using the U.S. dollar as their functional currency, and unrealized gains and losses on available-for-sale securities.

Customer Bankruptcy

In September 2017, Wynit Distribution (“Wynit”) filed for bankruptcy protection under Chapter 11 of the United States Bankruptcy Code. Wynit was the Company’s largest customer, historically representing 11% of total revenue during the six months ended July 1, 2017 and 19% of total accounts receivables as of July 1, 2017. In connection with Wynit’s bankruptcy filing, the Company believed that the collectability of the product shipments to Wynit during the third quarter of 2017 was not reasonably assured. However, as of July 1, 2017, collectability of accounts receivables from Wynit was reasonably assured.

The Company ceased to recognize revenue from Wynit, which totaled $8.1 million during the third quarter of 2017. Additionally, the Company recorded a charge of $35.8 million during the third quarter ended September 30, 2017 comprised of cost of revenue of $5.5 million associated with shipments to Wynit in the third quarter of 2017 and bad debt expense of $30.3 million associated with all of Wynit’s outstanding accounts receivables. The Company maintains credit insurance that covers a portion of the exposure related to its customer receivables. The Company recorded an insurance receivable based on an analysis of its insurance policies, including their exclusions, an assessment of the nature of the claim, and information from its insurance carrier. As of September 30, 2017, the Company had recorded an insurance receivable of $26.8 million, included in prepaid expenses and other current assets, associated with the amount it had concluded was probable related to the claim. The $26.8 million insurance receivable allowed the Company to recover $22.7 million of bad debt expense and $4.1 million of cost of revenue, resulting in a net charge of $9.0 million in the consolidated statement of operations comprised of net bad debt expense of $7.6 million and net cost of revenue of $1.4 million. The Company received $21.4 million of the insurance receivable during the fourth quarter of 2017, and the remaining $5.4 million in January 2018.

During 2018, the Company released $12.4 million in product return and rebate reserves related to Wynit, as it believes the possibility of future claims associated with these reserves is remote. This reserve release resulted in a $12.4 million increase in revenue during the year ended December 31, 2018.

Non-Monetary Transaction

The Company entered into an agreement with a third party during 2016 to exchange inventory for advertising credits and cash, which was amended in October 2018 to extend the contractual period from four to six years. The Company recorded the transaction based on the estimated fair value of the products exchanged. For the year ended December 31, 2016, the Company recorded $15.0 million of revenue and $7.0 million of associated cost of goods sold upon exchange of the products for advertising credits of $13.0 million and cash of $2.0 million. The $13.0 million of unused advertising credits remaining as of December 31, 2016 were recorded in prepaid expenses and other current assets, and other assets. Such credits are expected to be used over the contractual period of six years, and will be expensed as advertising services are received. During the year ended December 31, 2018 and 2017, $2.3 million and $0.8 million, respectively, of credits were utilized. The Company’s prepaid and other assets related to unused advertising credits as of December 31, 2018 and December 31, 2017 were $9.9 million and $12.2 million, respectively.