On its second night of the season, Fox's American Idol trounced every show in sight, but its audience was well below that for the comparable show a year ago. Wednesday night's two-hour Idol prelim averaged a 17.6 rating and a 26 share (30.28 million viewers) between 8:00 p.m. and 10:00 p.m. That compared to a 21.6/31 (36.94 million viewers) for the second night of the season last year -- a decline of nearly 20 percent. Still, the ratings for Idol beat the combined ratings for ABC, CBS, and NBC, whose ratings were also down from a year ago.