Once you have your idea in a tangible format, there are three things you can do to protect you against copyright infringement. First, contact your local copyright office and have it registered (there usually is a cost associated with this ). Second, register the document at the writer’s guild of America. This can be done online at www.wga.org (this usually costs $10). Third, have the document sealed in an envelope, and have it sent to you via registered mail. I’ve heard conflicting stories on whether or not this last method will hold up in a court of law. I would just do it anyways.