Does the detail need to be in a separate container? I may be misunderstanding your example, but I would have thought you could achieve what you wanted by adding the details section to the item template for your list items and then hiding/showing it based on the IsSelected flag:
<ListView ItemsSource="{Binding}">
<ListView.ItemTemplate>
<DataTemplate>
<DockPanel>
<ContentControl DockPanel.Dock="Right" Name="DetailsControl" Content="{Binding}" ContentTemplate="{StaticResource DetailsTemplate}" />
<TextBlock Text="{Binding}" />
</DockPanel>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding (ListViewItem.IsSelected), RelativeSource={RelativeSource FindAncestor, AncestorType=ListViewItem}}" Value="False">
<Setter TargetName="DetailsControl" Property="Visibility" Value="Hidden" />
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Even if you aren't after exactly this behaviour, I imagine you could get close to what you want by replacing the ContentControl from the example with something else (e.g. a Popup)