Write your idea into a full synopsis, treatment or television bible complete with character bios, possible future episodes and more. Have several people you trust read it and give you their feedback as they may have some good ideas that will inspire you to make changes.
Register your work with the Writer's Guild of America (see the link in the Resources section). This will show that you were the original creator of the idea so if anyone tries to claim it is theirs you can prove you created it because it is registered and dated under your name. This is easy to do online and costs 20 dollars.
Purchase a copy of the Writer's Guide to Hollywood Producers (see the site in the Resources section where this can be purchased). Go through the guide and mark all the producers and production companies seeking new television concepts. Read the submission requirements for each company: some request eemail queries and others want query letters, a synopsis or treatment.
Write a query letter introducing yourself and your concept and stating that if they are interested in your idea they can contact you at such-and-such address. Include your mailing address, e-mail address and a phone number. E-mail all those who accept e-mail queries and print letters for those who require snail mail submissions.
Wait for responses from companies interested in your idea. Some will ask to see some sample pages or a pilot or will call you in for a meeting. Prep for a meeting by creating a verbal one-minute pitch where you tell them all about your idea in one minute. Practice your pitch on your friends so you can get all your nerves out.