Add a column to a many to many relation table code first entity framework

I have 2 classes which have a many to many relation.

public class Document
{
    public int Id { get; set; }

    public string Name { get; set; }

    public bool AvailableOffline { get; set; }

    public string URL { get; set; }

    public virtual ICollection<Profile> Profiles { get; set; }

}

public class Profile
{
    public int Id { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }

    public virtual ICollection<Document> Documents { get; set; }
}

On each profile I wish to have a SortOrder field for each document. So I made the joined table explicit in another class

public class ProfileDocuments
{
    [Key, Column(Order = 0)]
    public int DocumentId { get; set; }

    [Key, Column(Order = 1)]
    public int ProfileId { get; set; }

    public int SortOrder { get; set; }

    [ForeignKey("DocumentId")]
    public virtual Document Document { get; set; }

    [ForeignKey("ProfileId")]
    public virtual Profile Profile { get; set; }   
}

But when I update the database the table for this last class will not have a column for SortOrder. It only holds the 2 foreign keys. How can I tell EF to generate this table with my column?