Insurance regulators in Washington state have regained the power to reject excessive premiums for individual health plans. Regence BlueShield, the state’s largest insurer for such plans, has begun mailing notices to 150,000 policyholders that rates will jump an average of 17.8% Aug. 1. Earlier, Seattle’s Group Health Cooperative notified about 20,000 customers with individual and family coverage that their premiums would rise almost 10% on July 1.The rate increases are the first to be vetted by state Insurance Commissioner Mike Kreidler under a new law that gives him authority to disallow "unreasonable" premiums on individual policies. But despite the newfound authority, thousands in state residents may still see double-digit rate increases this summer.