Stealth Camping in Idaho is legal if you follow the restrictions and common sense that is required in most other states.

You cannot stealth camp on fenced or posted land.  You cannot stealth camp on cultivated (unharvested) lands. 

You can stealth camp in areas that are not fenced, not posted, and are not unharvested and cultivated.

You should verify this with your own research including  laws and codes at the city, township, and county levels.