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: Mortgage insurer MGIC Investment (NYSE: MTG) dropped a whopping 20% in intraday trading today after reporting a large loss and massive earnings miss.

So what: For the second quarter, operating EPS was -$0.86, compared to the -$0.11 consensus estimate, and GAAP EPS was -$0.75. The cost of claims from mortgage defaults increased 44% to $460 million while the number of "cures" (insured borrowers that caught up on their mortgage payments) dropped 24% to 35,832.

Now what: Revenue from insurance premiums fell 8% to $285 million, reflecting tighter loan standards. The ratio of claims and expenses to premium revenue increased markedly to 1.78, from 1.19 in the year-ago quarter. With the press release offering no reason for optimism in the next few years, it's no surprise the stocks of competitors Radian Group (NYSE: RDN) and PMI Group (NYSE: PMI) are also down today.

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.