Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Greenbrier (NYSE: GBX), a maker of railcars, continued a slide that started yesterday falling as much as 11% in trading today.

So what: Quarterly numbers released yesterday were stronger than expected, but management's comments were cautious at best. An expected slowdown in the fracking market put a halt to higher trading yesterday and contributed to losses today. But the big catalyst was Susquehanna's lowering of its price target on the stock from $28 to $21.

Now what: Let's keep in mind that the company just crushed estimates and $21 per share is still a 24% upside from where shares are trading today. The market has certainly panicked over a potential slowdown in one of the company's end markets, which was running at such a frenetic pace that it would eventually have to slow down. Shares may be volatile for a few days, but I see this as a great buying opportunity for the long-term investor. The company has now crushed estimates for three straight quarters, and shares are trading at just 6 times next year's expected earnings. That sounds like a great discount to me.

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