Fast National ratings for Thursday, January 19, 2012.
 
The shrinking of the "American Idol" audience continued Thursday night, with a diminished-but-still-big "Idol" pulling FOX to a nightly win in the 18-49 year-old demographic, but falling behind CBS in total viewers.
 
For the night, FOX averaged a 3.9 demo rating and 12.3 million viewers, while CBS got a 3.5 in the demo (thanks to the resiliency of "The Big Bang Theory") and 14 million viewers overall. ABC was third (2.5, 7.1 million), followed by NBC (1.7, 4.2 million) and the CW (0.9, 2.2 million).
 
8 p.m. -- "Idol" averaged 17.7 million viewers and a 5.6 demo rating to easily win the hour for FOX in both measures, but the numbers were down 19 percent from the already-low Wednesday night premiere ratings, and down 27 percent from the first Thursday episode of last season. Then again, "Idol" tends to dip from its first night to its second, and the dip was proportional (the premiere was down 26 percent from the season 10 premiere).
 
"Big Bang Theory" (6.2, 15.7 million) was virtually untouched from last week's "Idol"-less number and actually came out slightly ahead of "Idol" in the demo for that first half-hour. CBS' "Rob" (3.6, 11.7 million) on the other hand, dipped from its premiere and is now retaining only 69% of the "Big Bang" lead-in (compared to 79 percent last week). ABC's "Wipeout" and NBC's comedies both averaged a 1.8 demo for the hour, but "Wipeout" had 5.9 million viewers to only 4.2 million for NBC. (From half hour to half hour, "30 Rock" was down a couple of percentage points from last week, and "Parks and Recreation" was up a couple, but neither shift was notable.) "The Vampire Diaries" (1.1, 2.7 million) brought up the rear for the CW.
 
9 p.m. -- ABC's "Grey's Anatomy" (3.4, 9.3 million) edged out CBS' "Person of Interest" (3.3, 14.3 million) in demos but was well behind it in total viewers. "The Office" and "Up All Night" combined to average a 2.4 and 5 million viewers for NBC, and "Up All Night" is now retaining only 65% of its lead-in numbers from "The Office." FOX's "The Finder" (2.2, 6.8 million) was up 30 percent from last week's disappointing debut numbers, when "Bones" was its lead-in, but it only retained 39% of the "Idol" young adult audience, whereas a year ago "Bones" held onto 50% of the "Idol" lead-in.
 
10 p.m. -- "The Mentalist" (2.9, 14 million) easily won the hour in both measures for CBS, followed by ABC's "Private Practice" (2.1, 6.1 million), and NBC's rapidly-sinking "The Firm" (0.9, 3.4 million), which is now down to "Chuck"-level numbers.
 
All ratings information comes from preliminary Fast National Nielsen data, which includes live and same-day DVR viewing. All numbers are subject to change.