As an interviewer, there are any number of prompts you can use to get job candidates to divulge more details and give you a more complete picture. When they have finished their response to your question and you want to know more, say:
Or, just remain silent for a moment or two. They’ll speak up to fill the void.
It bears repeating…
Find a way to keep in touch with the great people who have left your employ. Keep them on the company newsletter list or keep remembering their birthdays with a card. Let them know you’d welcome them back. You never know; the grass isn’t always greener.