If you think about it, building a company takes about 5 years (if everything goes right).
So essentially for someone to "steal your idea", it implies that they have to commit their next 5 years to it.
So really you can talk freely about your idea to anyone who hasnt already started a company and is working in a similar space or someone who has a vested interest in a company which is working in a similar space. Thats basically it.
Another thing google did was to never give out specifics - even the number of computers they used was a secret for the first 2 years after they became successful.
So essentially for someone to "steal your idea", it implies that they have to commit their next 5 years to it.
So really you can talk freely about your idea to anyone who hasnt already started a company and is working in a similar space or someone who has a vested interest in a company which is working in a similar space. Thats basically it.
Another thing google did was to never give out specifics - even the number of computers they used was a secret for the first 2 years after they became successful.