Complex sentence: In 1991, Stone joined Walder, Hayden & Brogan, a law firm in Roseland, New Jersey, where he became a partner and remained until February 2014, when he joined Brown Moskowitz & Kallen in Summit, New Jersey.
Split into simpler sentences: In 1991, Stone joined Walder, Hayden & Brogan, a law firm in Roseland, New Jersey, where he became a partner. In February 2014, Stone joined Brown Moskowitz & Kallen in Summit, New Jersey.