American Idol remained unstoppable Tuesday night as it averaged 25.10 million viewers, peaking in the third half hour with 25.96 million. The wonder is that the competition from CBS and NBC remained strong. In the 8 00 p.m. hour, CBS averaged 18.07 million viewers for NCIS, which NBC averaged 8.20 million for The Biggest Loser . At 9 00 p.m., CBS's The Mentalist registered 18.26 million viewers, while the second hour of Loser drew 9.61 million. CBS moved into first place at 10 00 p.m. as Without a Trace recorded 12.21 million viewers. NBC's Law & Order SVU closed the night for NBC with 9.45 million viewers. ABC placed a distant fourth for the night, averaging just 4.45 million viewers for the night.