Expedia Inc -- the Bellevue, Washington-based parent company of some of the world’s most popular travel websites -- announced Wednesday that it would buy vacation rental site HomeAway Inc., capping a series of increasingly expensive acquisitions. The $3.9 billion deal will bring it more directly in competition with its largest rival, Airbnb Inc.

Expedia will pay $38.31 for each share of HomeAway, a 20 percent premium over HomeAway’s closing price Tuesday. The deal, subject to regulatory approvals, is expected to close in the first quarter of 2016, the companies said, in the joint statement.

“We have long had our eyes on the fast growing $100 billion alternative accommodations space and have been building on our partnership with HomeAway,” Expedia CEO Dara Khosrowshahi said, in a statement. “Bringing HomeAway into the Expedia, Inc. family and adding its leading brands to our portfolio of the most trusted brands in travel is a logical next step.”

Over the past year, Expedia -- which owns sites like Hotels.com and Hotwire.com, and is currently valued at nearly $18 billion -- has undertaken several large acquisitions in order to compete with Airbnb -- which is valued at over $25 billion. In January, Expedia acquired its competitor Travelocity for a sum of $280 million. And, in February, the company shelled out $1.3 billion for Orbitz Worldwide.

While Airbnb typically offers short-term rentals and HomeAway often targets travelers looking for longer stays, buying HomeAway allows Expedia to expand its offerings to consumers beyond hotels, and brings it closer to Airbnb’s traditional territory.

HomeAway’s stock was up 21.7 percent in after-hours trading on Nasdaq as investors responded positively to the news, while Expedia’s shares rose 2.5 percent -- after closing down 1.6 percent Wednesday.