It is an idiom, but you're right. It's something people say when you've done a good job (plural, in this case).
What makes it awkward to translate is that molodets is a noun used in a context where English would supply a verb or adjectival phrase, plus there is not much connection between the meaning of the word (from "molodoi," young) and the way it is used. So its literal meaning is something like "youngster," but its actual meaning is closer to "way to go."
And now you know.
Got your file, TAS. I'll get it back to you when I can. The iPad is fine, but not for editing....
And I learned something new.