Setting global font family

Possible Duplicate:
How to set the default font for a wpf application?

Coming from a web development background I often get mixed up on how to assign styles to my controls. What I'd like to do is set a global font family for the entire application.

In my App.xaml file I have the following

    <Style TargetType="{x:Type Window}">
        <Setter Property="FontFamily" Value="Helvetica, Arial" />
        <Setter Property="FontSize" Value="13" />
    </Style>

I've tried changing the target type to Control but that's not doing anything. I would expect that since everything technically lives in a Window control that everything would work as expected.

Turns out the TextBlock control doesn't inherit from Control. I'm assuming that's most of the problem because 90% of my text is in TextBlock form.

In CSS I would do something like this:

body {
    font-family: Helvetica, Arial;
    font-size: 13px;
    }