Altice said early Thursday that would pay $34.90 a share in cash for Cablevision, valuing the deal at $17.7 billion including existing Cablevision debt. Altice said the price tag worked out to a multiple of 6.1 times earnings, assuming that the company will be able to realize some $900 million in cost savings by combining Cablevision's 2.8 million subscribers with the 1.5 million U.S. cable subscribers that Altice services through its acquisition of a majority stake in another U.S. operator, Suddenlink Communications, in May.

"As a family business we are proud to be entrusted by the Dolan family with the ownership of Cablevision and look forward to continuing the pioneering path they have paved for us," said Altice founder and president Patrick Drahi. "The strategy of Altice in the large and highly strategic U.S. market is reinforced with the acquisition of Cablevision. We will be in a stronger position, as in all other markets in which we operate, to deliver the best services, invest in the most advanced technology, and develop innovative products for the benefit of our customers."

The deal marks the end of an era for the cable business, as the Dolan family that control Cablevision been a seminal force in the growth of pay TV. Charles Dolan founded the company with 1,500 subscribers on Long Island in 1973. In a lengthy statement issued early Friday morning on the East Coast, CEO James Dolan, son of Charles, acknowledged that the deal was more than a routine big-bucks transaction.

"Since Charles Dolan founded Cablevision in 1973, the Dolan family has been honored to help shepherd our customers and employees through the most extraordinary communications revolution in modern history," Dolan sad. "Now, nearly half a century later, the time is right for new ownership of Cablevision and its considerable assets. We believe that Patrick Drahi and Altice will be truly worthy successors, and we look forward to doing all we can to affect this transition for our customers and employees. We expect that Cablevision will be in excellent hands."

Dolan emphasized that the sale of the cable systems serving New York's tri-state area -- principally coveted regions of Long Island where affluent subscribers pay for high-end services -- the Dolan family will still control the publicly traded media companies AMC Networks and the Madison Square Garden Co. Both were spun out of Cablevision in the past five years in what was a clear attempt to streamline the company's holdings for a sale of the largest asset. Madison Square Garden is in the process of splitting itself into two publicly traded entities, one for the company's sports teams and venues, the other for its MSG-branded regional sports networks.

"For the Dolan family, we move forward with AMC Networks and the Madison Square Garden Company - two and, eventually, three public companies - all born of Cablevision and each with brighter prospects today than ever before," Dolan said. "With profound gratitude to our employees, customers and shareholders who have made our vision a reality, the Dolans look forward to continuing this fascinating journey."

The Cablevision sale also includes the company's News 12 local news outlets, the Newsday media group that includes Long Island's home town daily newspaper, Newsday, and the company's media sales arm.

Cablevision shares shot up 16% in after-hours trading Wednesday after rumors of the deal began to spread. The stock closed Wednesday at $28.54.