This is an unprecedented challenge to the ACA. No one quite knows what is going to happen. Many critics are saying that it is illegal. One law professor even describing the attempt as "crazypants illegal" . The Republican-controlled federal government might just decide not to enforce this law anymore and leave Idaho unchallenged.
The real question is whether or not insurance providers will take the bite. The ACA fines companies $100 per day per violation. This could be an impractical business move for insurance providers if the federal government decides to enforce the ACA.