A Note on the Biblical Documentary Hypothesis
The strongest form of the Documentary Hypothesis—that Ezra wrote the whole thing—can be easily shown to be wrong.
According to the standard view, one reason to be suspicious of the traditional dating is that some documents refer to events that happened after their supposed date. If we assume that such was a common practice (it is a plausible explanation for the second half of Isaiah), a lengthy document which included numerous prophecies that did not refer to a very important event was probably written before the event.
The Torah makes no mention of the Divided Monarchy. I think we can date it to the time of Solomon or before even using the Documentary Hypothesis style of reasoning.
It's interesting that the seams are most visible in Genesis—which was written down centuries after the events even according to the traditional account. (I can imagine Moses collecting the legends of the Israelites, hearing one person say Noah sent out a dove, hearing someone else say Noah sent out a raven, and writing down that Noah sent out both … or maybe not.)
Another clue is that, if we rate the miracles in the Old Testament by unbelievability, the two most improbable miracles are the Flood and Joshua making the Sun stand still. Other miracles may have involved a temporary and local suspension of laws thought to be natural, but only the Flood and the Sun standing still would have left extensive evidence in non-Jewish traditions, evidence that doesn't seem to be there. By some coincidence, both of those events occurred long before they were written down, even according to the traditional account. If unbelievable miracles are the sign of delayed writing, clearly a lack of unbelievable miracles might mean the events were written down nearly immediately.
I suspect that the Documentary Hypothesis was an attempt by liberal Christians to pull the same stunt that seculars have been trying with the “Da Vinci Code” style of theorizing. They were better able to get away with it than the “Da Vinci Code” fans because there are more Christian scholars than Jewish scholars (cf. this discussion at EconLog for the effects of such a mismatch).
You can find other criticisms of the Documentary Hypothesis here.