How to change font via ExtendScript

Alright, there is probably a simple solution here, but I can't seem to change the font for a layer via ExtendScript. The CS6 scripting guide has me trying the following code:

var textProp = app.project.activeItem.layer(1).property("Source Text");

var textDocument = textProp.value;

textDocument.font = "TimesNewRomanPSMT";

Which I guess could also be written as:

app.project.activeItem.layer(1).property("Source Text").value.font = "TimesNewRomanPSMT";

The code executes without errors but the font in that layers remains with the previous setting.

Any ideas?