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 real estate investment trust Getty Realty (NYSE: GTY) took it on the chin today, falling as much as 13% in intraday trading after Getty Petroleum Marketing filed for bankruptcy protection.

So what: Something going wrong with Marketing -- as Getty refers to Getty Petroleum Marketing in SEC filings -- is something that should have always been on investors' radar. After all, it's the very first risk factor in the company's annual report:

Our financial results are materially dependent on the performance of Marketing. In the event that Marketing does not perform its rental, environmental or other obligations under the Marketing Leases, our business, financial condition, revenues, operating expenses, results of operations, liquidity, ability to pay dividends or stock price could be materially adversely affected. The financial performance of Marketing has deteriorated in recent years.

For 2010, Marketing accounted for two-thirds of Getty's revenue, and it appears that that customer-concentration risk has come home to roost.

Now what: Getty CEO David Driscoll had some relatively optimistic views on the Marketing bankruptcy, including highlighting the fact that the process going forward will be very defined and structured through the bankruptcy court. He also noted that acquisitions that Getty has made in 2011 helped the company further diversify its revenue stream, a timely move in light of the Marketing bankruptcy.

That Getty shares aren't selling off more than they are today probably suggests that investors were already preparing themselves for an adverse event from Marketing. Over the past year, Getty's stock price has fallen by close to 60%.

Now that those fears have been justified, it will be a question of just how costly the Marketing collapse will be for Getty and how quickly it can reclaim its property and start collecting from it again.

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