Idaho Code § 49-634: Limitations on overtaking on the left.

No vehicle shall be driven to the left side of the center of the highway in overtaking and passing another vehicle proceeding in the same direction, unless the left side is clearly visible and free of oncoming traffic for a sufficient distance ahead to permit the overtaking and passing to be completely made without interfering with the operation of any vehicle approaching from the opposite direction or any vehicle overtaken. In every event the overtaking vehicle must return to an authorized lane of travel as soon as practicable and in the event the passing movement involves the use of a lane authorized for vehicles approaching from the opposite direction, before coming within two hundred (200) feet of any approaching vehicle.