I found this online which makes it appear you don’t need anything unless you’re inside city limits.
Anyone 18 years of age or older who can legally possess a firearm can carry a concealed firearm outside the confines of any city in the state of Idaho on while in a motor vehicle anywhere in the state. Only Idaho Residents 18 or older and current members of the U.S. Armed Forces who can carry legally possess a firearm can carry concealed in Idaho including inside the confines of a city without a state issued permit/license to carry. Non-Residents must have a permit/license to carry issued by any other state to legally carry concealed outside a motor vehicle in cities in Idaho.