Last week, “American Idol” returned to the air for its seventh season and despite a drop-off in ratings from last year, it looks like it will continue to be a juggernaut for at least another season. Tuesday’s two-hour premiere more than doubled the ratings of ABC, CBS, and NBC and easily stands as the season’s No. 1 entertainment telecast. Still, it came in more than 10 percent below the previous year’s record-setting debut. However, any continuation of the writer’s strike in Hollywood bodes well for “Idol,” as first-run shows continue to evaporate.