I've been reading Julian Sheffield's essay, "The Father in the Gospel of Matthew," in A Feminist Companion to Matthew, edited by Amy-Jill Levine:
The term, father, is used for God 65 times in the synoptic gospels (Matthew, Mark, and Luke). 44 of those are in Matthew. God the father is identified as "heavenly" or "in heaven" 20 times in Matthew.
Sheffield instructs us that this interpretation of God as heavenly father comes from the context of Rabbinic prayer language. This language emphasizes who is in charge--God, not Caesar.