Fenway Partners, a New York private investment company, is acquiring Sleep Country USA, the Kent-based mattress retailer whose trademark jingle "Why buy a mattress anywhere else?" is known throughout the Northwest.

Terms of the deal, which the companies completed Tuesday, were not disclosed.

Robert Cook will remain chief executive of Sleep Country, which will continue to operate as an independent retailer. Cook's wife, Sunny Kobe Cook, who appears in the company's ads, will remain part of its senior management team, serving as a business and marketing consultant. Sleep Country executives also will retain an equity stake in the company.

No layoffs are expected at Sleep Country.

"Fenway Partners sees Sleep Country as a solid platform to expand into the Northwest with its strong management team and well-known brand name," said President Richard Dresdale.

With 28 stores throughout the Seattle and Portland markets, Sleep Country is one of the largest bedding retailers in the Northwest.

In January, Sleep Country Canada, a spin-off from its American counterpart, was bought by an investment group led by Boston-based Bain Capital in a $70 million deal.