The decision to transition the business behind Michael Kors’ fashion empire into a public company was a tough one for its CEO, John Idol.

“I didn’t want to go public,” Idol said during a speech at Wharton yesterday organized as part of Penn Fashion Week. “I’ve run four public companies, and the hardest thing to do when you run a public company is to not change the way you’re running the business because you have investors and, more importantly, Wall Street looking over your shoulder.”

But Idol and the firm’s leadership team ultimately decided to make the leap. The company debuted on the New York Stock Exchange in December, pricing its shares above estimates at $20 each, raising $944 million. The shares have more than doubled in value since, and last week the firm announced that it would sell more than $1 billion in stock in a secondary offering.

Michael Kors made the move with in order to build long-term value into the brand. “The hardest thing to say when you go public is that you’re going to do the right thing for the business over the next three to five years,” said Idol, who was previously an executive at Ralph Lauren, Donna Karan and Kaspar A.S.L. “Some investors don’t want to hear that. They want to hear what you’re going to do over the next quarter and the next month. But I guarantee that if you run a public company like that, you’re going to fail.”

When Idol and partners Lawrence Stroll and Silas Chou acquired the business in 2003, they, along with Kors, who acts as chief creative officer, had the goal of building it from a brand with a “cult following” to one that graced the closets of a global and multigenerational clientele. “[Michael Kors] was a $20 million business in 2004,” Idol said. “It was losing money and probably would have gone out of business had we not bought it.” The company now has a market cap of $8.6 billion. For the fourth quarter of 2011, it reported $373.6 million in revenue, a 68% increase over same time a year earlier, and net sales of $199.4 million, an 82.8% jump from 2010.

Michael Kors achieved his initial success designing apparel, but the company’s relatively rapid growth came from an unexpected source: accessories. “We looked for the white space in the market,” Idol said in an interview before his speech. “The pure luxury accessories market was a crowded field with Prada, Louis Vuitton and others, but in the accessible luxury market there was Coach and not a lot of other competitors.” Idol added that today, around 70% of Michael Kors’ business comes from selling shoes, bags, eyewear and watches.

The company bills itself as a purveyor of jet-set luxury, and Idol says the team always keeps in mind its target customer. “Michael has a simple saying. When I say, ‘Michael, who is our target customer?’ he says, ‘She’s 35 years old,’” Idol noted. “I ask him, ‘How do you know?’ and he says, ‘Any woman who is 50 wants to be 35 and any woman who is 25 wants the wardrobe of a 35-year-old.’”

Today, the company includes the signature Michael Kors line that walks the runways each season, competing with brands such as Gucci and Dolce & Gabbana, and the more affordable Michael line. In Michael Kors stores, $2,000 handbags share the display cases with purses priced at $200 or $300. Addressing the Penn audience of mostly 20-somethings, Idol noted that, “You guys will go into H&M or Zara and buy a top and buy a jean, but you’re also going to call your mom or dig deep into your savings and try to get a Gucci bag. You’re going to mix high and low, and you don’t feel embarrassed that you bought a Forever 21 top.”

Unlike many retailers that have reached a saturation point in the U.S. market, with around 180 or 190 stores nationwide (out of 230 globally), Michael Kors still has room to grow, Idol said. “When we get to 500 stores in the U.S., that will be an opportunity to have some dialogue. Coach is there today — they’re doing $2.7 billion or $2.8 billion in the U.S., and they’re probably not completely saturated in the U.S. because the handbag business, the accessory business, continues to grow. When you look at the market and see they’re doing $2.7 billion to $2.8 billion and we’re doing $1 billion in the U.S., then I think we’re at about the halfway point. It shows you can maintain a brand’s integrity and still grow to that size.”

The company is also eyeing more expansion into global markets, but Idol stressed the need for a measured strategy. “China today for us is the most expensive market to hire people in. Why? Because everybody wants to go to China, and for the mid- and upper-tier executives, it’s a field day. Secondly, real estate is insane. Why? Because everybody’s going there. Prices are through the roof, and the logistics are not easy. It’s not like the U.S. and Europe where the logistics have been set for years and years and years. This is the wild, wild West.”

In addition, brand awareness can’t be built overnight. “In China or Japan, people don’t understand what Michael Kors is; it literally means nothing,” Idol said. “It’s a very challenging thing, a very expensive thing, to do and you have to be patient and have the vision of 10 years. We’re a wealthy company, we have the money to do it and we have to do it because to be global we must undertake that endeavor. But you can’t enter a country and think you’ll be successful just because you’re a big, bad American company.”