This study examines the association between XBRL extensions and financial information environments of firms, where “financial information environment” refers to the degree to which a firm's financial information is reflected in the information held/used by investors. An XBRL extension is a customized definition of a financial concept or reporting situation that is not available in the U.S. GAAP Financial Reporting Taxonomy. In 2009, the U.S. Securities and Exchange Commission (SEC) allowed firms to begin to use extensions to add new concepts in their financial disclosures. Critics express concerns that the reporting discretion permitted under the XBRL mandate will reduce comparability of financial disclosures and complicate financial analysis. Proponents contend that XBRL extensions will provide users with new and relevant information. To evaluate the competing views, we employ several proxies for financial information environment and perform analyses for early and later phases of XBRL adoption. We find that XBRL extensions are negatively (positively) associated with financial information environments of firms at the early (later) phases of XBRL adoption. The results for later periods of XBRL adoption provide support for the SEC's policy that allows registrants to use XBRL extensions to increase users' understanding of the information in financial statements.