Cox Enterprises Inc., an Atlanta-based conglomerate, on Thursday said it had closed on its $4 billion acquisition of Dealertrack Technologies Inc., one of Long Island's largest and fastest-growing software makers.

Cox, which also owns Kelley Blue Book, paid $63.25 per share in cash for the Lake Success company, which makes programs for auto dealers.

"This combination brings together some of the best people in the industry with strong common values," Dealertrack chairman and chief executive Mark O'Neil said in a statement issued by the two companies.

Earlier Thursday, Dealertrack closed on a deal to sell its platform of automotive inventory tracking software, Inventory+, to a California company for $55 million. The sale, to DealerSocket of San Clemente, California, was required to settle an antitrust suit and secure approval from the U.S. Justice Department for the Cox merger.

Cox's acquisition of Dealertrack continues a trend of Long Island losing its public companies. More than 30 local businesses with stock traded on major exchanges have either transferred their headquarters elsewhere, shut down or been acquired since 2007.

Dealertrack, founded in 2000 in Garden City, is among the biggest successes in the effort to attract and grow high-tech companies here.

The company has more than tripled its annual revenue, to $854.4 million, since 2010. Analysts predict 2015 sales will rise to more than $1.097 billion. And last fall, Dealertrack broke ground on a 233,000-square-foot headquarters in North Hills and agreed to add more than 350 jobs in exchange for more than $19 million in state and county tax breaks and grants.

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Dealertrack has said the acquisition does not change the company's plans to move into the facility in 2017. Cox, meanwhile, has said there are no plans to reduce Dealertrack's workforce, which includes 4,400 people, with nearly 550 on Long Island.