One of the things I have noticed about Berkshire is that everybody has a capital gain (today), a lot of stock is in taxable portfolios, some of the unrealized capital gains are ridiculously substantial.

Since the BNSF deal there has been a lively options market on BRK.B and since Berkshire pays no dividend there are those that use a covered call strategy above the stock.

When Berkshire breaks to new highs, we tend to get these types of follow-through moves as people adjust their positions because they sure-as-hell do not intend to be called out of their low basis stock and pay the tax man.

Also, Insurance stocks are on fire right now and Berkshire tends to break out right before the market sells off in a sort of last ditch flight to quality type thing.