The top U.S. mutual savings bank is going public.

Goldome, based in Buffalo, N.Y., is the last of the nation’s top 20 thrift institutions to take the step. Mutual savings institutions are owned by their depositors, while stock institutions are held publicly by those purchasing their stock. Ross B. Kenzie, Goldome’s chairman, said the stock offering was expected to raise between $265 million and $350 million. Goldome has 120 branch offices in New York and Florida and subsidiary operations nationwide. Assets total $14.6 billion. The bank has $11.01 billion in deposits, $10.13 billion in loans and reported a record profit of $52.9 million last year.