Ok, i was thinking about this. This might sound complete cr@p but i'll put it out there and you can tell me what you think.
I think you have to bet more on the turn. It's likely the guy has it here because of the speed he reraises, however he could have pulled an excellent bluff on you here.
You bet 4k into a 9.4k pot so it looks weak (this is where i might expect hesitation from the guy while he considers bluffing your weak bet). This may be feigned weakness so he wants to fnd out. So he raises to 12k (into a 16k pot, this is good because he only has to make one decent sized stab to find out). This 12k really represents the rest of your stack so now he's really asking you a question here. If he has got it he knows he can push for your last 8k (and you call) on the river and if he doesn't he is going to check-fold the river and save himself 8k (obviously if you move in he only calls with the goods). Whats the minimum you are calling with here? 2pr or a set. Are you going to back one pr and draw with your stack (he might have you on 7-8). If he had a diamond draw i think he would push rather than bet only 12k. The point is that it's only 12k to him (as chip leader) and 20k to you.
If you bet 6-8k then the guy can only reraise you for your entire stack. This is going to seem less appealing to him because 8k into a 9.4k pot looks stronger. It is far less likely to be a bluff and you find out where you are (the problem is that 8k is a lot to you).
I think you can poke holes in this but he can't have you on a straight, only 2pr or a set whereas he knows you know he could have anything.
Just my (overthought) opinion.
yeah i can see this however....(assuming the guy is a decent player and not like Flushy states somewhere a mug)
he comes form the bb so can have any 2 cards. he bets on the flop...( i am thinking he's open ended) and calls the reraise...this really shouts open ender to me as it is how I might play it.
when the 7 comes he checks...flushy bets and he reraises..essentially asking flushy for his entire stack. This to me again confirms that (If he's a decent player) he has now made the straight and want to get cash before the flush can hit.
it's a fair bet (the 4k) and it's a good fold...IMO.
again..this is of course assuming the guy knows how to play poker.