Get a lawyer, and if you hire a programmer, force him to sign an NDA, which means that, if he steals your idea, you can sue him. Plus you may want to put him on a contract so he sticks around to finish the job.
No self respecting developer signs NDA's.
An idea is worth nothing unless you can bring it to market and sell it.
Wtf ... Any self respecting programmer with "start-up" xp will not get involved unless the paperwork and NDA's are in order!
Get things right first time around, there are meany sharks out there that will steal code and/or idea's without blinking. Speaking from xp here: first time over a year, second time months of work/time gone because the paperwork wasn't in order. (third time ? sorry guy's not gone happen)
On top of that if you have no xp with ether start-ups or programming learn some of the basics before you get in, then you at least know the in/out's before you start talking to people ... don't be the idea guy to meany of those around, learn the skills to execute at least the basics. (experts to finish/complete things can be hired later)
You are in luck as well, coursa Startup Engineering starts on Monday. It will cover all aspects of doing a basics web start-up (don't let programing part scare you, basics are not that hard at all)
https://www.coursera.org/course/startup