Did the writers of the gospels get their information from other sources?

There are many who claim that Matthew, Mark, and Luke all got information from a source that predates them known as document Q.  They claim that this is why these three gospels are so similar to each other.  However, the only evidence for Q is in the minds of those who believe it.  There is not a single manuscript, fragment, or written record that confirms that such a document ever existed.  In fact all of the evidence for Q is taken from the text of scripture.  The goal of this biased line of thinking is to undermine scripture and cast doubt on its authority.  This is one of the oldest tricks in the book by the devil to deceive people to turn from God (Genesis 3:1)