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 credit insurer Radian Group (NYSE: RDN) won't help pay your mortgage today; the share price has tanked to the tune of 12% today on above-average trading volume.

So what: Fellow mortgage insurance providers MGIC Investment (NYSE: MTG) and PMI Group (NYSE: PMI) also crashed hard today. MGIC sparked the slide by reporting a wider first-quarter loss than expected.

Now what: MGIC's troubles spell bad news for the entire mortgage insurance industry, because the terrible results stem from a sudden rise in claim payouts. A rising tide lifts all boats, but a bone-dry riverbed also leaves everybody equally stranded. Nearly 14% of MGIC's insured mortgage loans are currently delinquent.

Interested in more info on Radian Group? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. 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 is investors writing for investors.