There has been a recent furor over movie studios stealing script ideas, and there seems to be a fear among the young that game devs might steal ideas, too. People want laws made! People want action taken!
People want to shoot themselves in the foot!
I know people who work in fairly high positions in fairly large companies. They regularly (often more than once a week) get mailed or emailed by someone who has "the bestest idea".
Because of the way the law works for non-creative-media companies, these appeals aren't even looked at. They are returned unopened, often with a "have your lawyer contact us" stamp. Why? Because if the company ever produces anything vaguely similar, they get sued. Difference between patents and copyrights, I guess. I'm not an expert.
I think that is just a fantastic idea to apply to the movie industry. Yeah! Instead of suffering the tiny chance that your script gets stolen, you should instead save yourself by simply being unable to get anyone to read your script in the first place. Whoa! Great fuckin' solution there, boys!
Here's the thing: ideas, and even whole scripts, are pretty much useless. In order for something to have any merit, it not only has to be good, it has to fit in a slot.
When you pitch a script or a game bible to a production company, you're not really pitching that script. You're pitching your ability. The script is just a script. It's simply proof that you can write (or design). Is it gonna get stolen?
Well, it's unlikely, but maybe. Who cares? It's not your freaking baby, it's a script. As a professional, you should be able to produce endless varieties of scripts for anyone willing to drop money on your desk.
The power of being a pro isn't that you've got a great idea. It's that you have a hundred thousand great ideas, and you have new ones every time someone says, "I need a..."
The power of being a pro isn't in any given production, it's in the fact that you can reliably produce.
Now, if you pitch a mostly completed movie or game to one of these companies, and they steal that, well... that's far, far more serious shit. Those are largely completed products as opposed to ideas barely even stamped on paper.
It's also extremely rare, easy to prove, and easy to sue for. Those might be related facts.
So, IMO, don't worry overmuch about your ideas being stolen. It probably isn't going to happen. If it does, it'll be a slap in the face, but at least you know you're in the right skill bracket. Also, it's fairly likely that there was another, virtually identical idea pitched at roughly the same time. You'd be amazed at how often two or three versions of the same weird-ass idea roll into a studio.
Your power isn't in that paper you wrote. It's in the fact that you can write the paper they want you to write. That's true of game design, it's true of script writing, it's even true of fiction and nonfiction writers, although in a more roundabout way.