PORTLAND — The Maine Employers’ Mutual Insurance Co. will issue an $18 million dividend to about 17,000 policyholders based in Maine.

That dividend amount is the highest in the Portland-based company’s history, topping a $16 million dividend issued last year to Maine employers, which equaled about 13 percent of premiums.

This year’s dividend is based on the company’s performance in 2011 and equals 14.4 percent of the premiums paid in that year. The company provides insurance for more than 20,000 employers with about half of its premiums coming from outside of Maine, according to Michael Bourque, a senior vice president with MEMIC.

“It’s clear that our strategy to grow along the Eastern Seaboard is literally paying dividends to the members of our mutual company in Maine,” said John Leonard, MEMIC’s president and CEO.

The company opened its eighth office in the past year, in Tysons Corner, Virginia, and plans to take in more than $250 million in premiums by year’s end, up from $230 million last year. It has licenses to write premiums in 46 states and the District of Columbia.

While the annual dividend stands to rise with a growing amount of written premiums, if the company maintains the percentage it can return to employers, Leonard said in the statement that improved safety and collaboration also plays a role.

“This is what can happen when employers and employees work together to reduce injuries and keep costs low,” Leonard said.

According to the Maine Department of Labor, injuries and illnesses at privately insured workplaces in Maine declined 3.8 percent from 2010 to 2011 and have declined further since then. From 2011 to 2013, that rate declined another 3.3 percent. The number has declined during the past four years.

The company reported its average dividend check will be $1,040 this year, the first time it is has been more than $1,000. The amount of specific dividend checks depends on how much an employer pays in premiums.