Give away the idea to several people in the hopes that they hear the idea and want to work on it.
If I share the idea, I make no money from it. If I don't share, I might one day have enough time to implement it myself, or run into people I can trust 100%. If these are the only options, I HAVE TO choose the latter, and not share it for now :-(
If what you are doing right now isn't as valuable as the idea, then why not work on it (right now, with someone you trust) instead?