Arch Capital Group Ltd.’s fourth-quarter net income rose 150% to $316.0 million, as most metrics, including combined ratio and gross written premiums, improved during the period, the Bermuda-based insurer and reinsurer reported Tuesday after the markets closed.

Net premiums written rose 11.8% from the year-earlier period to $1.45 billion, Arch said in a statement. The company’s combined ratio improved to 83.8%, compared with 87.8% in the year-earlier period, the statement said.

Underwriting income jumped 50.6% to $251.4 million, while net investment income rose 3.7% to $119.9 million.

Results included a favorable development in prior-year loss reserves of $54.7 million, the statement said.

In the insurance segment, net premiums written grew 28.7% to $688.7 million, and the combined ratio improved to 102.1% from 102.8% in the year-earlier period. The growth came from new businesses acquired during 2019, new business initiatives or product lines, expansion of existing products and accounts, and rate increases across most lines of business, the statement said.

While property/casualty rates are increasing, “the market remains in a transition phase between softer and harder conditions,” Mark Grandisson, president and chief executive officer of Arch, said on the company’s Wednesday morning earnings call. Such conditions, he said, are likely to continue in the foreseeable future.

Arch’s insurance and reinsurance businesses are well positioned for the pricing improvements taking place, Mr. Grandisson said.

In the reinsurance segment, net premiums written increased 4.3% to $338.9 million, and the combined ratio improved to 93.8% from 110.9% in the year-earlier period. The growth in net premiums written primarily reflected increases in property lines from new business and growth in existing accounts, the statement said.

In the mortgage segment, net premiums written increased 2.0% to $347.7 million, and the combined ratio improved to 21.6% from 22.6% in the year-earlier period. The growth in net premiums written primarily reflected an increase in monthly premium business due to growth in insurance in force, the statement said.

Mr. Grandisson said the mortgage insurance market was healthy.

For all of 2019, net income rose 123.0% to $1.59 billion.

Full-year net premiums written grew 16.1% to $5.51 billion, and the combined ratio improved to 79.7% from 81.0%, according to supplementary financial data.

Full-year net investment income rose 12.1% to $491.1 million.