The Boston Bruins signed defenseman Dennis Seidenberg to a contract extension on Thursday, rewarding the defensemen that twice helped them reach the Stanley Cup finals with $16 million over the next four years.The team announced the deal between periods of its opening night game against the Tampa Bay Lightning."He's been one of our core guys since we got him," general manager Peter Chiarelli told reporters. "'D' like Dennis are hard to find. The way that he plays, it's hard to find."The deal, which has an average cap value of $4 million, would keep Seidenberg in Boston through the 2017-18 season. He said it gives him a no-trade clause for the first 30 months, with a limited no-trade clause over the next 30 months.Chiarelli said this week that signing Seidenberg, who could have become a free agent at the end of the season, was the organization's top priority."I wanted to be here. They wanted me here. Both sides gave a little bit," Seidenberg said after the Bruins opened with a 3-1 victory over the Lightning. "I'm really happy to be here for five years."In 10 NHL seasons, plus one game, Seidenberg has 34 goals and 154 assists. As Zdeno Chara's partner on the Bruins' No. 1 defensive pairing, Seidenberg helped Boston win the Stanley Cup in 2011.Seidenberg was sixth in the NHL in blocked shots and was third among defensemen with a plus-18 last season, when the Bruins returned to the finals, losing to the Chicago Blackhawks in six games.