Custom RichTextBox and Text Property Binding

Question

I have created a custom RichTextBox control and exposed a Text property. The Text property is defined as follows:

 public string Text
        {
            get
            {
                return new TextRange(Document.ContentStart, Document.ContentEnd).Text; 
            }
            set
            {
                AppendText(value); 
                OnPropertyChanged("Text");
            }
        }

The RichTextBox is using a ViewModel as DataContext as shown below:

<WPF:SharpRichTextBox MaxCharactersAllowed="100" NotificationStyleName="defaultTextBlockStyle"
                              Text="{Binding Path=Name, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
                              DefaultNotificationStyleName="textblockStyle" Margin="10,10,10,10" Background="Yellow">
        </WPF:SharpRichTextBox>

Now I want that whenever I change the Text of the RichTextBox the "Name" property in the ViewModel gets updated. How can I do that?