There are two possibilities:
- Your idea is not actually very innovative
- Your idea is truly revolutionary
In addition, two main groups may or may not take it:
- Big companies
- Indie developers
Let us see how this play out:
1-1. A big company has nothing to take from your idea, they already have a backlog of ideas to do in the near future (or sequels to do, har har), and there is people pitching ideas to them regularly. For a big company, ideas are cheap. They do not need to go out taking ideas from individuals, much less, if they are not far from what is already in the industry.
1-2. Chances are the other developers have their own pet projects for which they have passion. Without a wow concept, the only indie developers that may take yours are those who lack ideas of their own... more on this later.
2-1. You have a crazy new concept. It is too much of a risk for a big company to try to copy it before knowing it will work. On the other hand, if you can make a proof of concept and get some publicity, you try to get people or companies to invest in you. Therefore, in this case you should not fear big companies. Just make sure any attention the game gets is associated with you.
2-2. If you got a great concept, in theory somebody may try to rush you to the market. In this case, you may want to be vague until you can say you are actually working on it.
On the work ethics of indie developers, indie developers are people. There have to be a few with little regard for others as in any group.
In general the risk only exist if they perceive your idea as better as theirs and their own talent as better than yours, because that's the situation in which they may win at rushing to the market.
You are going to mitigate this in two ways:
Once you start getting help on your game, pay attention on your language, you aren't a guy with a concept and no idea how to make it... you are working on your idea and you are looking for help.
Everything you do about the game must have your name. Set up a blog; make presence in social media, etc. If somebody else comes up with the same thing, we will all know who is stealing from who, and you will have evidence that you were working on this beforehand.
This will convince others that you are taking this project seriously, which will suggest that it will be harder to rush you to market. In addition, if they do, you have how hold your ground (on one hand because you reached people first, and on the other because they have any legal battle lost♪).
♪: They will not risk a legal battle; they have not reached success yet. Remember that those that may even consider this are not big, and have poor ideas. These are generalizations, of course.
I do not know the future, so I cannot really tell if people will try to steal your idea. In general, other indie developers will more likely want to work with you if they want to work on your concept than try to steal it. Besides, most ideas gets replicated once the pioneer showed that it was a good idea not before.
For abstract: own your game idea. As in, make it clear it is yours.
Are you wondering what would happen, if it fails? Pff, who cares, people will forget about it soon enough. It the game is bad, you would have reached only a small fraction of the people you will reach when eventually you make a good game (so most of those will not know your prior failure).
You are still learning, c'mon! Who can blame you‽ -- me
On that note, every indie developer that has reached fame (that I know of), did not get it on his or her first project.
Release early. Release often. And listen to your customers. -- Eric S. Raymond
It takes twenty years to make an overnight success. -- Eddie Cantor