I know a lot of people think people/companies wont steal your idea, however, for me, that is completely context dependent. A big company... well no, I agree. However, a seed funded tech start up, circling in your industry and still searching for a solid business model.....? Too trusting!!
You should be so lucky that someone will steal your idea. The truth is that its all about execution and not ideas. Facebook wasn't the first social network, they just executed better. Same for Instagram, Yammer and Airbnb - all Billion dollar companies built in public.