Summary of Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation—The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”). The financial information as of December 31, 2019 that is included in this quarterly report is derived from the audited consolidated financial statements and notes for the year ended December 31, 2019 included in Item 8 in our annual report for the year ended December 31, 2019. Such financial information should be read in conjunction with the notes and management’s discussion and analysis of the consolidated financial statements included in our annual report. The unaudited consolidated interim financial statements, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of March 31, 2020, the statements of comprehensive loss and stockholders' equity for the three months ended March 31, 2020 and 2019, and the statement of cash flows for the three months ended March 31, 2020 and 2019. The results for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any interim period or for any other future year.
Principles of Consolidation	Principles of Consolidation—The unaudited consolidated interim financial statements include the accounts of Redfin and its wholly owned subsidiaries, including those entities in which we have a variable interest and of which we are the primary beneficiary. Intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates—The preparation of consolidated financial statements, in conformity with GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and results of operations during the respective periods. We evaluate our estimates on an ongoing basis. In January 2020 we adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326), which modifies the measurement of credit losses on financial instruments. As part of the adoption we estimated the current expected credit losses for certain classes of relevant assets. The amounts realized from the affected assets will depend on, among other factors, general business conditions, including the impacts from COVID-19, and could differ in the near term from carrying amounts reflected in the consolidated financial statements. Further description of the impact of this pronouncement is included in Recently Adopted Accounting Pronouncements.
Accounts Receivable and Allowance for Credit Losses	Accounts Receivable and Allowance for Credit Losses—We have two material classes of receivables: (i) real estate services receivables and (ii) receivables from the sale of homes. Accounts receivable related to these classes represent closed transactions for which cash has not yet been received. We establish an allowance for expected credit losses based on historical experience of collectibility, current external economic conditions that may affect collectibility, and current or expected changes to the regulatory environment in which we operate our real estate services business. As the majority of our transactions are processed through escrow, collectibility is not a significant risk, and we have determined the nature of our receivables to have similar credit quality indicators. We evaluate for changes in credit quality indicators on an annual basis or in the event of a material economic event or material change in the regulatory environment in which we operate, with the most recent assessment being performed in March 2020.
Investments	Investments—We have two types of investments: (i) available-for-sale investments that are available to support our operational needs, which are reported on the balance sheets as short-term and long-term investments, and (ii) long-term equity investments accounted for under the cost method, which are reported in other non-current assets. Available-for-sale Our short-term and long-term investments consist primarily of U.S. treasury securities and other federal or local government issued securities, all of which are classified as available-for-sale. Available-for-sale debt securities are recorded at fair value, and unrealized holding gains and losses are recorded as a component of accumulated other comprehensive income. Available-for-sale securities with maturities of one year or less and those identified by management at the time of purchase to be used to fund operations within one year are classified as short-term. All other available-for-sale securities are classified as long-term. We evaluate our available-for-sale securities, both ones classified as cash equivalents and as investments, for expected credit losses on a quarterly basis. An expected credit loss reserve is charged against the fair value of an available-for-sale debt security when it is identified, with a credit loss charged against net earnings. We review factors to determine whether an expected credit loss exists based on credit quality indicators, such as the extent to which the fair value as of the reporting date is less than the amortized cost basis, present value of cash flows expected to be collected, the financial condition and prospects of the issuer, adverse conditions specifically related to the security and any changes to the credit rating of the security by a rating agency. Realized gains and losses are accounted for using the specific identification method. Purchases and sales are recorded on a trade date basis. Cost Method Investments In December 2018, we purchased an equity interest in a privately held company for approximately $2,000, which is classified as long-term. The investment is an equity security without a readily determinable fair value that is accounted for at cost minus any impairment, plus or minus changes resulting from observable price changes in orderly transactions for identical or similar investments of the same issuer. We perform a qualitative assessment considering impairment indicators to evaluate whether the investment is impaired as of the end of each reporting period.
Advertising and Advertising Production Costs	Advertising and Advertising Production Costs—We expense advertising costs as they are incurred and production costs as of the first date the advertisement takes place.
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements—In January 2020, we adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326), using a modified-retrospective approach. The adoption of this guidance requires a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The pronouncement, along with the related subsequent pronouncements that include clarifications, modifies the measurement of credit losses on financial instruments. This guidance requires the use of an expected loss impairment model for instruments measured at amortized cost based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The adoption of this pronouncement did not have a material impact on our consolidated financial statements. See specific accounting policies for accounts receivable and available-for-sale debt securities previously discussed in this Note 1, and see Note 2 and Note 3 for additional impacts from the adoption. Recently Issued Accounting Pronouncements—Recent accounting pronouncements issued by the Financial Accounting Standards Board (including its Emerging Issues Task Force), the American Institute of Certified Public Accountants, and the Securities and Exchange Commission did not have, or are not expected to have, a material impact on our present or future consolidated financial statements.

Summary of Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of Presentation—The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”).

The financial information as of December 31, 2019 that is included in this quarterly report is derived from the audited consolidated financial statements and notes for the year ended December 31, 2019 included in Item 8 in our annual report for the year ended December 31, 2019. Such financial information should be read in conjunction with the notes and management’s discussion and analysis of the consolidated financial statements included in our annual report.

The unaudited consolidated interim financial statements, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of March 31, 2020, the statements of comprehensive loss and stockholders' equity for the three months ended March 31, 2020 and 2019, and the statement of cash flows for the three months ended March 31, 2020 and 2019. The results for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any interim period or for any other future year.

Principles of Consolidation

Principles of Consolidation—The unaudited consolidated interim financial statements include the accounts of Redfin and its wholly owned subsidiaries, including those entities in which we have a variable interest and of which we are the primary beneficiary. Intercompany transactions and balances have been eliminated.

Use of Estimates

Use of Estimates—The preparation of consolidated financial statements, in conformity with GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and results of operations during the respective periods. We evaluate our estimates on an ongoing basis. In January 2020 we adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326), which modifies the measurement of credit losses on financial instruments. As part of the adoption we estimated the current expected credit losses for certain classes of relevant assets. The amounts realized from the affected assets will depend on, among other factors, general business conditions, including the impacts from COVID-19, and could differ in the near term from carrying amounts reflected in the consolidated financial statements. Further description of the impact of this pronouncement is included in Recently Adopted Accounting Pronouncements.

Accounts Receivable and Allowance for Credit Losses

Accounts Receivable and Allowance for Credit Losses—We have two material classes of receivables: (i) real estate services receivables and (ii) receivables from the sale of homes. Accounts receivable related to these classes represent closed transactions for which cash has not yet been received.

We establish an allowance for expected credit losses based on historical experience of collectibility, current external economic conditions that may affect collectibility, and current or expected changes to the regulatory environment in which we operate our real estate services business. As the majority of our transactions are processed through escrow, collectibility is not a significant risk, and we have determined the nature of our receivables to have similar credit quality indicators. We evaluate for changes in credit quality indicators on an annual basis or in the event of a material economic event or material change in the regulatory environment in which we operate, with the most recent assessment being performed in March 2020.

Investments

Investments—We have two types of investments: (i) available-for-sale investments that are available to support our operational needs, which are reported on the balance sheets as short-term and long-term investments, and (ii) long-term equity investments accounted for under the cost method, which are reported in other non-current assets.

Available-for-sale

Our short-term and long-term investments consist primarily of U.S. treasury securities and other federal or local government issued securities, all of which are classified as available-for-sale. Available-for-sale debt securities are recorded at fair value, and unrealized holding gains and losses are recorded as a component of accumulated other comprehensive income. Available-for-sale securities with maturities of one year or less and those identified by management at the time of purchase to be used to fund operations within one year are classified as short-term. All other available-for-sale securities are classified as long-term. We evaluate our available-for-sale securities, both ones classified as cash equivalents and as investments, for expected credit losses on a quarterly basis. An expected credit loss reserve is charged against the fair value of an available-for-sale debt security when it is identified, with a credit loss charged against net earnings. We review factors to determine whether an expected credit loss exists based on credit quality indicators, such as the extent to which the fair value as of the reporting date is less than the amortized cost basis, present value of cash flows expected to be collected, the financial condition and prospects of the issuer, adverse conditions specifically related to the security and any changes to the credit rating of the security by a rating agency. Realized gains and losses are accounted for using the specific identification method. Purchases and sales are recorded on a trade date basis.

Cost Method Investments

In December 2018, we purchased an equity interest in a privately held company for approximately $2,000, which is classified as long-term. The investment is an equity security without a readily determinable fair value that is accounted for at cost minus any impairment, plus or minus changes resulting from observable price changes in orderly transactions for identical or similar investments of the same issuer. We perform a qualitative assessment considering impairment indicators to evaluate whether the investment is impaired as of the end of each reporting period.

Advertising and Advertising Production Costs

Advertising and Advertising Production Costs—We expense advertising costs as they are incurred and production costs as of the first date the advertisement takes place.

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements—In January 2020, we adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326), using a modified-retrospective approach. The adoption of this guidance requires a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The pronouncement, along with the related subsequent pronouncements that include clarifications, modifies the measurement of credit losses on financial instruments. This guidance requires the use of an expected loss impairment model for instruments measured at amortized cost based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The adoption of this pronouncement did not have a material impact on our consolidated

financial statements. See specific accounting policies for accounts receivable and available-for-sale debt securities previously discussed in this Note 1, and see Note 2 and Note 3 for additional impacts from the adoption.

Recently Issued Accounting Pronouncements—Recent accounting pronouncements issued by the Financial Accounting Standards Board (including its Emerging Issues Task Force), the American Institute of Certified Public Accountants, and the Securities and Exchange Commission did not have, or are not expected to have, a material impact on our present or future consolidated financial statements.