In ID Cruz had a higher percentage of endorsements by Senators, congressmen, St Sen, St Reps, etc than normal .... especially since Rand Paul dropped out. ID tilts libertarian.
Idaho also tilts toward the Christian identity movement and skinheads, and white supremacy. Right wing extremists groups abound in Idaho.
Any states with large Mormon populations may lean Cruz in the west.
ID also has a high percentage of Mormons, so I suspect that maybe Romney and crazy Glenn Beck might have some influence there.
Idaho is a sure thing in the general. So far Cruz has proven he can win in states we will take anyway.