If there was no justified reason to get fired and no documentation, can I sue my employer for wrongful termination?

Idaho is what is called an "at-will" employment state.  This means that an employer can terminate an employee at anytime for any reason or for no reason at all.  They are not required to tell you why they chose not to keep you, only that they are ending the employment relationship.

However, there are a few exceptions under the employment laws in Idaho to the at-will employment doctrine.  The first is if the employee can show that they actually had some type of employment contract for a certain term.  Vague discussions are not enough.  The second exception is if the employee for terminated for an unlawful purpose-- i.e. for being a whistleblower, for discriminatory purposes, etc.  If you have information that would support the termination was for an invalid purpose, then you could sue for wrongful termination.  If you have not filed for unemployment-- you might start there.  If they decide to oppose your receipt of benefits, then they must give a reason to the unemployment comp agency.