Probably Baptist like Westboro.
It seems to be part of a larger group that is part of the overall Baptist Convention, but they are strong on separation of church and state. From Wiki...
Mainstream Baptists is a network of Baptists in fourteen (U.S.) states that have organized to uphold historic Baptist principles, particularly separation of church and state, and to oppose Fundamentalism and Theocratic Calvinism within the Southern Baptist Convention.