(AP) - Officials at St. Luke's Health System say they are cooperating with an investigation by the Idaho attorney general's office and the Federal Trade Commission into whether federal antitrust laws and Idaho's Competition Act have been violated.  The investigation involves the health system's acquisitions of medical practices that have made it one of Idaho's largest employers, possibly running afoul of federal and state laws intended to prevent monopolies that reduce competition. Idaho Attorney General Lawrence Wasden in a February letter notes the health system's possible purchase of the Saltzer Medical Group as a complicating factor, and asks the health group to hold off on the purchase. Health system spokesman Ken Dey says health system officials have done everything properly.