Newport Beach-based Alliant Insurance Services Inc. has agreed to be acquired by New York-based investment firm Kohlberg Kravis Roberts & Co. LP on undisclosed terms.

Alliant is the largest insurance broker in Orange County by revenue. Its local operations had $54.5 million in annual revenue last year.

The insurance brokerage firm had been part of the Blackstone Group LP since 2007, when the New York-based investment and advisory firm bought it for a reported $1.1 billion.

Alliant employees own about 45% of the company and will roll over most of their stakes, according to a statement.