The idea stealing myth originates from people (cubicle drones) who have so few ideas of their own, that when they finally have one, since it seems so scarce to them, it obviously must be valuable and thus worth "stealing". Unfortunately, this kind of people also lack the ideas necessary to realize the few "precious" ones they have.

Who does have a chance of realizing them, are people with lots of ideas, also about how to actually implement ideas. However, when you reach and surpass the "idea a day" treshold, while being able to implement maybe 1 or 10 each month, you get to discard hundreds of your own ideas each year, making them pretty much worthless.

So you should never be afraid of sharing your ideas; whoever you're telling them to, will either not care, or fail miserably trying to "steal" them. In each case you're safe. As for the monthly surplus ideas, if you're not implementing them, you risk nothing by sharing them either... except maybe feeling dumb in the off chance of seeing someone else successfully implementing an idea you thought was worthless.

PS: in the even rarer case of sharing an idea you're implementing, and someone else beating you to it... you suck, do something at what you suck less.