CoStar, the D.C.-based commercial real estate data giant that has acquired at least 26 smaller companies on its way to becoming a $9B behemoth, has just made another acquisition.

In a $385M deal announced Tuesday, CoStar acquired multifamily advertising company ForRent, a division of Dominion Enterprises. The deal included $350M in cash and $35M in CoStar stock.

ForRent has 3.5 million monthly unique visitors across its four multifamily websites, ForRent.com, AFTER55.com, CorporateHousing.com and ForRentUniversity.com, CoStar said in the announcement. Based in Norfolk, Virginia, ForRent has 38 offices across the country and 475 total employees.

The acquisition will bolster CoStar's already massive network of websites used for searching apartments. In 2014, it acquired Apartments.com, which had 7 million monthly unique visitors at the time, for $585M in cash. In 2015, it acquired ApartmentFinder.com for $170M. CoStar plans to feature ForRent.com properties on Apartments.com, but will maintain each of the websites as distinct brands. It also plans to integrate the underlying technology that supports all of the websites by mid-2018, so advertisers can use a single platform to list apartments on each service.

"For the investors and lenders relying on CoStar for multifamily information and analytics, we expect the addition of properties and data from ForRent will further strengthen our information offering," CoStar CEO Andrew Florance said in a release.

CoStar's pattern of gobbling up competitors has led some of its competitors to accuse it of monopolistic behavior. Xceligent in June launched an antitrust lawsuit against CoStar, filed as a counterclaim to CoStar's December intellectual property suit, alleging it had engaged in years of anticompetitive behavior.

That legal battle has since ramped up with Xceligent issuing subpoenas to top brokerage firms CBRE and Newmark Knight Frank, and with CoStar bolstering its legal team with a top antitrust attorney.