When you get a good idea it's a good idea to outline. Although outlining is tedious, it is sometimes worth the effort. It is worth the effort because you will find you have a general idea of the direction of your story before you begin the laborious effort of filling in the minor details. Nothing kills plot like getting stuck in the murky bog of details, not to be confused with a pond full of cattails. An outline is supposed to work for you as a bicycle works for its rider and a hammer works for the builder. It isn't immovable or permanent. Rather, it is a rough sketch like the slight, soft pencil strokes of an artist finding his figures and figuring out his forms and forming his project. Your pencil sketch outline of a story's basic tune to which you'll add harmonious notes is no more confining than the chair in which you've most recently been seated. It helps to have a basic draft of how the story's going to move. After that you can add ideas by the dozens and spice and pepper up the plot where it needs more action or motion or emotion or drama or handsome actors or beautiful heroines or endearing animals.
That's it. Write on.