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 property and casualty insurer Harleysville Group (Nasdaq: HGIC) were climbing up into rarified air, soaring as much as 86% in intraday trading after Nationwide agreed to buy the company.

So what: When a potential buyer comes knocking at your door offering to pay a massive premium of nearly double your stock price, what do you do? Duh! You say "yes." And that's exactly what Harleysville said when privately held Nationwide offered to pay $60 per share for the publicly held Harleysville group (Nationwide is also merging with Harleysville Group parent Harleysville Mutual). I'd think it'd be tough for shareholders to be too distraught about this deal since this is a huge premium to both today's price and the stock's prerecession price.

Now what: As of this writing, Harleysville's stock is trading at just a bit more than 2% below the $60 offer price. That means if shareholders stick around through the close of the transaction -- which is expected to be in early 2012 -- they'll pocket an additional 2% and change for their patience. The decision on whether to hang on for that bump lies largely in whether investors see better returns opportunities elsewhere.

Meanwhile, for investors that are watching this from the sidelines, the purchase could sound a bullish note for property and casualty insurer stocks. Nationwide's offer values Harleysville at more than twice its most recently reported book value. So what does that say about stocks like Markel (NYSE: MKL) and W.R. Berkley (NYSE: WRB) that are trading at respective multiples of 1.05 and 1.04?

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