After the initial authentication using the JetBrains Account credentials, permanent Internet access is not required to use the product. It is required, however, that a product is able to connect to the JetBrains servers at least once every 30 days. If the last successful connection was within the mentioned 30 days, no interruptions should occur. In case no connection could be established for 30 days, the product will notify the user and will require some time to connect to the Internet before closing the application.
If you do not have access to the Internet at all, you can use an offline activation code. Please see How will the subscription-based licensing model affect customers who are unable to utilize electronic delivery or web-accessed software? for more information.