Berkshire Hathaway's ( BRK.A) Columbia Insurance unit said Tuesday it agreed to buy two California insurance-services companies for an undisclosed sum. Warren Buffett's investment vehicle will take control of American All-Risk Insurance Services and American Commercial Claim Administrators, which are both currently owned under the holding company Acacia Pacific Holdings. AARIS and ACCA provide underwriting and claims-management services for California workers compensation cases. Both companies already have an alliance with Berkshire's National Liability & Fire Insurance, which has been writing its California workers' compensation business through AARIS since 2004. The acquisition is expected to close this month.