How you choose to define growth goes a long way toward deciding just how good of a quarter Commerce Bancorp (NYSE:CBH) had. Most of your typical bottom-line measurements don't look so hot for the quarter that ended in December, but there's undeniable evidence that the company continues to build its business at a rapid rate.

Revenue for the quarter rose 6%. Now, "revenue" is kind of a goofy concept for bank stocks -- in this case, though, it means the sum of net interest income and non-interest income, including investment gains and losses. If you strip out those gains and losses, as some would suggest you should, you see growth in excess of 11%. Net income, too, is a little hazier than usual. Reported net income dropped 38% in the quarter, but there was a $19.3 million charge -- and backing that out reduces the net-income drop to 12%.

Net interest income, meanwhile, rose 7% in the quarter, as ongoing growth in assets offset a nasty decline in net interest margin. While it's admittedly still very early in the bank reporting season, Commerce's drop from 4.16% to 3.52% (and from 3.67% in the third quarter) is one of the sharpest I've seen so far. Nevertheless, while the bank's cost of funds has gone up considerably, it still stands at a very competitive 2.01% -- and that's better than even notoriously cheap US Bancorp (NYSE:USB) or cross-selling specialist Wells Fargo (NYSE:WFC).

If you're looking for growth this quarter from Commerce, you'll find it in loans and deposits. Average loan balances grew more than 30% in the fourth quarter, and average deposits were up 24%. Simply put, those are incredible growth rates. Unfortunately, though, that growth is coming at a cost -- non-interest expenses climbed 27% in the fourth quarter as a byproduct of the company's aggressive expansion strategy.

This is an unusual banking stock, and it has a sometimes-fanatical investor base. I understand the virtues of growth, and I also get the notion that Commerce is approaching the banking business with a very different strategy. That said, sooner or later the old "it's different this time" argument wears a bit thin, and the results ultimately are what they are. In this case, you have a bank spending a lot of money to grow its business, and it remains to be seen whether management can drive sustainable profitability when the expansion boom slows down -- as it eventually will.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).