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 Zions Bancorporation (Nasdaq: ZION) fell 10% today after the company released disappointing earnings.

So what: Adjusted earnings per share came in $0.03 short of estimates at $0.30 per share, helped by the release of $1.5 billion in loan-loss reserves. Just for good measure, Stifel Nicolaus downgraded the company from buy to hold.

Now what: It's not surprising the stock dropped after a very disappointing earnings report. The company's net interest margin declined sequentially, something analysts at Jefferies & Co. expect to continue in coming quarters. I just can't see a good reason to jump on this drop today and would wait to see improvement in results before buying this stock.

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