When to leave the table

I'm wondering if I'm leaving money on the table. My attitutde up to this point has been to leave when I double my money, but I'm wondering if I should stay longer to try to squeeze more money out of a session. When is the right time to leave the table? I ask because I have stayed in the past when I'm up, trying to turn a profit into a bigger profit, only to lose what I had. Thoughts?