Minneapolis-based Apogee Enterprise surprised analysts with better than expected financial results last Wednesday and on Thursday, its stock rose more than $5 a share to $48.78.

When you look at all the glass covered tall buildings in Minneapolis, think of Apogee. The company makes the aluminum architectural framing and glass for the “curtain walls” that face such buildings. It also makes curtain walls and covered the nation’s largest building, the new World Trade Center One building in New York, in 2016.

Apogee has quietly grown over the years from its beginnings as Harmon Glass in 1949. Today it operates 8 companies, 12 U.S. manufacturing/fabricating locations and 13 similar operations elsewhere (including 11 in Canada). It employs more than 7,000 people.

Last week it reported revenues of $336.5 million for its first quarter. This was a 24 percent increase from a year ago due in part to an acquisition it made since then. Operating income was down $22 million, from $24 million a year ago. But overall results were better than analysts expected and—combined with management’s declaration that results will be even better going forward—led to a gain in the company’s stock price.

Investors may want to wait before buying in, however: The company still has to get its costs in line as it further consolidates after acquiring a business last year. While revenues rose 24 percent, costs rose more, leading to an overall drop of 9 percent in operating income to $22 million for the quarter, compared with $24 million made on less revenue a year earlier.