If for example the character you chose to analyse was Dionysus; you could say that he shows humanism when he free's the maenads from Pentheus's jail-like closure and through the way that he (initially) gives Pentheus a chance to reconsider his actions, stating "My friend a happy settlement may still be found." (Page 219).
As for the rationale aspect, that is much the same as what I have said above; it is quite difficult to say anything else humanist/rationale about Dionysus as he is very excessive with pride and succumbs to arrogance especially during the end of the play.
For idealism, you could say that Dionysus parallels effeminacy and therefore he somewhat displays women as powerful through his feminist traits- which is controversial to individual's of that time, given that era but which glorifies women. You could also say that Dionysus' stand against opposition is somewhat idealist in the way that he doesn't just cower away from forces that avenge him.
I hope this helped in some way!! :-)