C# WPF ошибка доступа из потока к RichTextBox.Document через Dispatcher

private void Button_Click(object sender, RoutedEventArgs e)
{
    new Thread(() =>
    {
        FlowDocument doc = new FlowDocument();
        Paragraph paragraph = new Paragraph();
        paragraph.LineHeight = 2;
        paragraph.Inlines.Add(new Bold(new Run("11111"))
        {
            Foreground = Brushes.White,
            Background = Brushes.Black
        });
        doc.Blocks.Add(paragraph);
        rr(doc);
    }).Start();
}
private void rr(FlowDocument d)
{
    this.richtextbox1.Dispatcher.Invoke(DispatcherPriority.Normal, new Action(() => {
    this.richtextbox1.Document = d;  }));
}

выдает ошибку:

"The calling thread cannot access this object because a different thread owns it."

тоже самое если попробовать richtextbox1.Document.Blocks.Add(paragraph). А вот richtextbox1.AppendText(text) идет без проблем.