The new owners of the Mauna Lani hotel and golf courses on Hawaii island rehired all employees when the deal closed Tuesday and said they plan to invest between $70 million and $90 million upgrading the resort.

An affiliate of San Francisco-based ProspectHill Group called DiamondHead Land bought the Mauna Lani Bay Hotel & Bungalows, the Francis H. Ii Brown Golf Courses and other property including undeveloped land for an undisclosed price.

Patrick Fitzgerald, partner at DiamondHead Land, said Tuesday that the new owners plan to make substantial improvements to their new assets, which previously belonged to a subsidiary of Japanese-based Tokyu Corp. that had owned the property for all of its more than 40-year history.

“Our goal over the next three to six months is to formulate our improvement plans and then share them with staff and with county agencies for approvals,” Fitzgerald said. “This will be the largest renovation on the property to date. I think the previous owners did a $25 million renovation in the early 2000s.”

Fitzgerald said preliminary renovation plans will focus on improving the property’s atrium, making it a communal gathering place where people can meet to bask in the sun, have drinks or attend receptions. The new owners also are considering adding lunch and dinner service to the hotel’s Bay Terrace restaurant, which is regularly open only for breakfast, he said.

“We’ll also be adding an adult and family pool and doing some landscaping at the South Lawn or Great Lawn,” Fitzgerald said. “And, we’ll make room improvements and improvements to the golf course and clubhouse.”

He does not expect that the hotel will add a “great deal of rooms,” but said it might create additional suites.

As part of the deal, DiamondHead Land had the option to rehire the resort’s roughly 500 employees, and did so.

Fitzgerald said employees of the previous owner did not have to reapply for jobs and were rehired at the same pay and benefits.

“We wanted to make the transition as seamless as possible,” he said.