Meiji Yasuda Life Insurance Co. agreed to buy U.S. insurer StanCorp Financial Group Inc. for about $5 billion, joining Japanese insurers that are expanding abroad to counter the shrinking domestic market.

Meiji Yasuda will pay $115 a share for the Portland, Oregon-based insurer, a 49.9 percent premium on its one-month weighted-average share price, according to a statement.

Japanese insurers are looking for ways to spread risks and increase revenue overseas as an aging population saps demand for policies and natural disasters lead to higher payouts. Tokio Marine Holdings Inc. agreed to buy HCC Insurance Holdings Inc. for about $7.5 billion last month. Dai-Ichi Life Insurance Co.’s paid about $5.5 billion for Protective Life Corp. this year.

“This continues the process” of Japanese insurers pursuing takeovers abroad, David Threadgold, an analyst at Keefe Bruyette & Woods in Tokyo, said by phone. Japan’s demographics mean that “if you stay at home, you’re a shrinking company.”

StanCorp was founded more than 100 years ago and sells a range of products that companies offer to their employees, like long-term disability and life insurance. It also offers annuities.

Its profit has climbed as it benefited from higher premiums in its employee-benefits unit and improvements in the individual-disability business. The insurer said Thursday that net income rose 58 percent to $64.3 million in the second quarter from a year earlier.

Securing Revenue

Meiji Yasuda Deputy President Hiroaki Tonooka said the purchase price was appropriate considering StanCorp’s growth potential. The Japanese insurer will “make a comprehensive decision” if a good deal comes up in the future, he said.

“Particularly for large Japanese life insurers, the total amount of insurance in force is declining, so bringing a quality overseas insurer under the umbrella is a good way to secure stable revenues and diversify portfolios,” said Reina Tanaka, a credit analyst at Standard & Poor’s in Tokyo.

StanCorp’s shares had rallied almost 10 percent this year, before the acquisition announcement. That compares with a 1.2 percent drop for the Bloomberg Industries North America Life Insurance Valuation Peers Index.