get the type of doc stored in TDocStd_Application

Say I have a few subclass of TDocStd_Document, then use TDocStd_Application::NewDocument() to add instances of those subclasses. (I've subclassed TDocStd_Application as well):
Handle_FooDoc fooDoc;
myApp->NewDocument("foo", fooDoc);
Handle_BarDoc barDoc;
myApp->NewDocument("bar", barDoc);

I then iterate over the docs:
for (int i=1; iNbDocuments(); ++i) {
Handle_TDocStd_Document doc;
myApp->GetDocument(1, doc);
// how do I determine the type of doc?
// doc->IsKind(STANDARD_TYPE(FooDoc)) never succeeds
}

Ive attached a short compilable example.