Hi Eber, as developers, we receive dozens of ideas in a single month. If were for stealing ideas, well, we won't afford to build all the good ones. Everyone have great ideas, not everyone has the will and the means to make them become reality.
Besides, you got NDA's, contracts, and such. As a rule of thumb, we always say there are 3 more entrepreneurs out there with your very same ideaa, so hurry up. Google wasn't the first search motor, facebook was not the first social network, skype was not the first messaging service and so on. You are the most important piece at your idea. The second most important is the technological partner you choose. Google their references, ask your friends or colleagues, or just ask to have a call and check other apps they did. BUT take heed on some special detail: how they understand your idea, whether they propose alternative solutions and how they solve problems. Ideas are the first step, polishing the second, drafting and pitching them the third, developing is the fourth, and marketing the fifth. Test developers in each of those steps and you will know beforehand what kind of developer you have in front of you.