Group Health Cooperative CEO Scott Armstrong stepped down after Kaiser Permanente completed its acquisition of the cooperative, the Seattle-based Puget Sound Business Journal reported, citing a spokesman.

Susan Mullaney will head Group Health Cooperative, which will be named Kaiser Foundation Health Plan of Washington in the coming weeks, according to the report. Mullaney has served at Kaiser Permanente for nine years.

It was Armstrong's decision to leave the company, the news publication said.