Not to mention that an idea is just an idea, and means absolutely nothing. It is your execution, your writing itself, that will determine a stories success or failure. Games are the same. Really anything is the same. Good ideas with poor execution will fall a lot faster then bad ideas with good execution.
Much further into development you can be worried that someone might steal your idea, but again it's a very very VERY small possibility. Backup your work on external drives and online. Keep a record of the work you do. That'll cover you for the most part.
And to me, I wouldn't care even if someone did steal my story (or game). Sure, they're now making money off of it. But it would mean my game had what it takes, and if that's true I can make many more - because the one stealing it cannot replicate you, and you are what made that story or game. Though I have an odd perspective on things, so I doubt saying that will help you.