Plastic interior door casing

Bear with me on my description ... but my interior door leading to the bathroom has a plastic molding around it. It is the type that has a "lip" all the way around it and covers about a 1/2 in perimeter of the entire door minus the bottom. All that being said I hit the molding/casing with my knee and snapped off a 3in. piece it. Does anyone know what this type of casing is actually called and where it can be purchased? Thanks in advance for any help or suggestions for a viable replacement. PS it's only about an 1 1/2 wide.