They attract each other.
When the charged insulator (regardless of whether + or -) is brought near an uncharged metallic object, electrons will migrate on the metallic object so that the area near the charged insulator is the opposite charge (and, by conservation of charge, the area of the conducting object away from the insulator will have an excess of the same charge as the insulator).
Because opposite charges attract and the opposite charge on the conducting object is closer, the dominant force will be one of attraction.
If they are allowed to touch, the conducting object will then have the same charge as the insulator and the objects will repel.
