I have a rental lease that is meant for the state of Idaho but I live in the state of Washington and the lease agreement is only signed by me is is a valid document?

If you are the temant , yes... the landlord can sign their copy at any time. What differences would be in it in Idaho that would be different in Washington State?

No state has a specific form for rentals. You probably have one printed by a real estate broker. There may be terms in one state that only apply in that state. If you want to go over landlord tenant law in both states and see if anything doesn't gibe, feel free. It never hurts to know the law of the state you live in anyway.