Allied World Assurance Co. Holdings A.G. recorded a dip in net income but experienced improved underwriting results in the fourth quarter as the company continued to expand its offerings globally and capitalize on increasing rates in the U.S. casualty insurance market.

The Zug, Switzerland-based insurer and reinsurer on Wednesday reported net income of $130.5 million for the fourth quarter of 2014, down 5.4% from the same period a year earlier. Net written premiums improved by 9.4% to $427.7 million for the fourth quarter compared with the fourth quarter of 2013. The company's combined ratio improved to 79.3% in the fourth quarter, compared with 92.0% in the fourth quarter of 2013.

Allied World President and CEO Scott Carmilani said efforts to diversify the company's businesses both geographically and by line of business were paying dividends. For example, the company's writings in the casualty market helped offset falling rates in its property business, he said.

“On average the rates across our insurance portfolio were up about 1% for the quarter, overall casualty rates were up 3%, and property rates were down around 9%,” Mr. Carmilani said during a conference call with analysts Thursday. “In the fourth quarter, much of the growth came from our casualty lines including excess casualty, environmental and programs.”

Mr. Carmilani said the rates in casualty lines continue to be especially robust in North America. “Notably, this is now the 10th consecutive quarter that we have achieved rate increases that have exceeded 5% in our U.S. casualty books,” he said.

However, the company fared less well in its reinsurance segment, as net written premiums for the reinsurance segment decreased 46.3% in the fourth quarter to $40.8 million compared with the fourth quarter of 2013.

Mr. Carmilani said the company chose to not renew certain accounts that did not meet pricing thresholds. “Reinsurance has been a steady contributor to our bottom line, and although we continue to be cautious about how we deploy capital in the segment, I am pleased with the overall performance,” he said.

On a yearly basis, the company fared better as net income rose to $490.3 million for the 2014 fiscal year, up 17.6% from 2013, net written premiums rose 9.4% to $2.32 billion from 2013, and the company's yearly combined ratio improved to 85.2% for 2014 compared with 86.2% in 2013.

Going forward, the company will look to expand its operations globally, Mr. Carmilani said, noting that in the past year Allied World expanded existing operations in London and Miami, opened new offices in Australia and Toronto and made acquisition in both Hong Kong and Singapore.