Grant Thornton Advisors announced Wednesday it has entered into a definitive agreement to acquire CBIZ (NYSE: CBZ), a professional services firm listed on the New York Stock Exchange, in an all-cash transaction with an enterprise value of $5 billion. Under the terms of the deal, CBIZ shareholders will receive $55.00 per share, representing a 54% premium to the company’s 30-day volume-weighted average price and roughly an 18% premium to CBIZ’s most recent closing price. The transaction is described as the largest of its kind in more than 25 years.