WPF Table Column Sizes

I'm rendering a Table in a WPF FlowDocument using code-behind. But, I've been unable to find an example that shows how to make the table use only the space needed based on content. Instead the table takes up all available width, which I don't want, nor do I want to have to specify a exact pixel sizes.

I'm clearly missing something simple, anyone see it?

var fd = new FlowDocument();

Table t = new Table();

t.BorderBrush = Brushes.Black;
t.BorderThickness = new Thickness(2);

// I thought this would do what I wanted...
t.Columns.Add(new TableColumn() { Width = GridLength.Auto });
t.Columns.Add(new TableCOlumn() { Width = GridLength.Auto });

TableRowGroup trg = new TableRowGroup();

TableRow currentRow = new TableRow();
currentRow.Cells.Add(new TableCell(new Paragraph(new Run("ABC"))));
currentRow.Cells.Add(new TableCell(new Paragraph(new Run("XYZ"))));
trg.Rows.Add(currentRow);

currentRow = new TableRow();
currentRow.Cells.Add(new TableCell(new Paragraph(new Run("123"))));
currentRow.Cells.Add(new TableCell(new Paragraph(new Run("789"))));
trg.Rows.Add(currentRow);

t.RowGroups.Add(trg);

fd.Blocks.Add(t);