If you are paraphrasing an idea from another work, you only need to include reference to the author and year of publication in your in-text citation. Although it is not required, APA guidelines encourage you to also provide the page number.
In the following example, the author summarized an article with an unknown author [The Wall Street Journal. (1994, January 10). Investors Have a New Tool for Judging Issuers’ Health: Cash-Flow Adequacy.] and cited the original source directly within the text. In a case like this where no author is listed, include an abbreviated article title/website title in quotation marks, or book title in italics. In general, when you are missing a key piece of information, you’ll need to include another detail that will allow the reader to identify the source.