Investment banker Piper Jaffray (NYSE:PJC) expanded its municipal debt business Wednesday, when it purchased Seattle-Northwest Securities in a transaction valued at approximately $21 million.

Calling Seattle-Northwest "an established leader in underwriting municipal securities," and one with a "nationwide" municipal bond sales and trading business, Piper CEO Andrew Duff said his firm is taking "a significant step forward in developing a national franchise for our business."

Investors may disagree. Piper shares traded down 0.9% on Wednesday, closing at $32.32 ahead of the buyout news. They haven't yet had a chance to react to the news that Piper is paying 1.6 times tangible book value for Seattle-Northwest, versus Piper Jaffray's own P/TBV ratio of 1.0.

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