You can sue only IF you had them sign some sort of nondisclosure or confidentiality agreement before you disclosed or shared the idea with them, which agreement stated that they could not take or use your idea themselves. If they signed such an agreement, you can sue them for breaching it; in the lawsuit, you can seek a court order barring them from using your idea and/or monetary compensation. But you need to have such an agreement, which they are violating; if someone does not contractually agree to not use your idea, they may take and use it; disclosing an idea to someone without a non-disclosure, etc. agreement is very dangerous, since the law does not otherwise protect business ideas.