What happened

Shares of M&T Bank (MTB 1.66%) were trading roughly 12.9% lower as of 12:56 p.m. ET Wednesday after the bank delivered disappointing results for the third quarter.

So what

M&T Bank reported diluted earnings per share of $3.53 on total revenue of roughly $2.25 billion -- both numbers that missed analysts' consensus estimates. It completed its  large acquisition of People's United Bank earlier this year, and is still in the process of integrating it into its operations.

Net interest income -- the profit banks make on loans and securities after covering the costs of funding those assets -- jumped by close to 19% compared to the second quarter, but also undershot analysts' estimates. Total loan balances also fell sequentially, even as many large banks have been reporting loan growth.

The institution's credit quality, however, still looks quite clean. Loan losses only ticked up slightly in the quarter, and total non-performing assets (such as loans that are delinquent by 30 or 90 days) actually declined from the second quarter. The bank took a provision for credit losses of $115 million in the quarter, which included a $52 million reserve build.

Now what

I'm not exactly sure what's driving such an intense dip in the stock Wednesday, as the earnings report doesn't look all that bad other than those big misses on estimates.

It's not great that its loan growth has slowed or that its net interest income was below expectations, but M&T Bank just completed a major acquisition. As such, it may take analysts a little while to determine how to accurately model its results again. Given that its credit quality remains quite healthy, and based on what is known right now, I am not all that worried by this bank's Q3 results.