Nature of Business	12 Months Ended
Nature of Business	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business AppFolio, Inc. ("we," "us" or "our") provides innovative software, services and data analytics to the real estate industry. Our industry-specific, cloud-based solutions are used primarily by property managers, and also by numerous other constituencies in the property management business ecosystem. These other constituencies include property owners, rental prospects, tenants and service providers, whom we refer to collectively as "users". Although specific functionality varies by product, our core solutions are designed to enable our customers to digitally transform their businesses, address critical business operations and enable exceptional customer service. In addition to our core solutions, we offer an array of optional, but often business-critical, Value+ services that are designed to enhance, automate and streamline processes and workflows that are essential to our customers' businesses. Our Value+ services are generally available on an as-needed basis and enable our customers to adapt our offerings to their specific operational requirements. Our solutions and services are designed to be a system of record to automate essential business processes, a system of engagement to enhance business interactions between our customers and their business ecosystems and a system of intelligence designed to leverage data to predict and optimize business workflows in order to enable exceptional customer experiences and increase efficiency across our customers' businesses. Our mobile-optimized software solutions are designed for use across multiple devices and operating systems. Our software solutions are offered as a service, are hosted using a modern cloud-based architecture, and in part, use artificial intelligence technologies. This architecture leads to rich data sets that have a consistent schema across our customer and user base and enables us to deploy data-powered products and services for our customers and users. For the years ended December 31, 2020, 2019 and 2018, our revenue was $310.1 million, $256.0 million and $190.1 million, respectively of which $284.7 million, $231.1 million and $172.4 million, respectively, are derived from our software and services offered to the real estate vertical. During certain periods covered by this Annual Report, we also provided software solutions and services to the legal vertical. On September 30, 2020, we completed our divestiture of 100% of the issued and outstanding equity interests of MyCase, Inc. ("MyCase"), a former wholly owned subsidiary that provided such legal practice and case management software solutions to our legal customers. We sold MyCase to Mockingbird AcquisitionCo Inc., a Delaware corporation (“Buyer”) affiliated with funds advised by Apax Partners LLP, for $193.0 million pursuant to a Stock Purchase Agreement, dated September 7, 2020 (the “Purchase Agreement”), by and among Buyer, us and MyCase (the “MyCase Transaction”). In connection with the closing of the MyCase Transaction, and in accordance with the terms of the Purchase Agreement, we entered into certain ancillary agreements with MyCase, including relating to certain post-closing transition services to be provided by us to MyCase at fair market value, as well as an intellectual property licensing agreement for certain software and patents for which no ongoing licensing fees will be received. We recognized a pre-tax gain on the sale of $187.7 million on the MyCase Transaction.