Fox’s ”American Idol” ruled as Thursday’s top program in demos and total viewers, showing its first week-to-week gains of the season. Also on the night, CBS’ ”The Big Bang Theory” still finished on top of ”Idol” head-to-head in demos at 8, and ABC’s ”Grey’s Anatomy” was on the rise while NBC’s ”The Office” drooped.

According to preliminary national estimates from Nielsen, ”American Idol” averaged a 5.7 rating/16 share in adults 18-49 and 17.9 million viewers overall in the 8 o’clock hour, finishing a close second in demos to ”The Big Bang Theory” at 8 before surging to a dominant lead at 8:30 (6.2/16). The 5.7 rating is an improvement over the prior two weeks for ”Idol” (5.5) and matches its premiere on Jan. 19 (5.7); and based on previous weeks, the show should edge up to a 5.8 in the nationals for its best Thursday score of the season. The net continues to fall off, though, at 9 p.m. with sluggish rookie drama ”The Finder” (2.3/6 in 18-49, 6.5 million viewers overall), whose softness seems to be helping competing dramas ”Grey’s Anatomy” and ”Person of Interest.”

Though it won only one half-hour in 18-49, Fox led Thursday in the demo, with CBS a close second and the night’s leader in 25-54 and total viewers.

At CBS, the steady ”Big Bang Theory” had another impressive showing kicking off the night (5.5/16 in 18-49, 16.1 million viewers overall), matching its season high in 18-49 , and perhaps setting a new mark if it edges up as usual in the nationals. The rest of the night continues to perform well for the Eye too, with ”Rob” (3.4/9 in 18-49, 11.0 million viewers overall) a solid second at 8:30 and ”Person of Interest” (3.3/8 in 18-49, 15.1 million viewers overall) matching its season-high 18-49 score of last week, placing second for its hour in 18-49 and leading in 25-54 (tied with ABC) and total viewers. And ”The Mentalist” has been above average of late too (2.9/8 in 18-49, 14.4 million viewers overall), standing as the No. 1 broadcaster in the 10 p.m. hour in all key categories.

ABC isn’t doing much in the leadoff hour with ”Wipeout” (1.6/5 in 18-49, 3.9 million viewers overall), but ”Grey’s Anatomy” (3.9/10 in 18-49, 10.1 million viewers overall) picked up steam to win the 9 o’clock hour in demos and remain the night’s No. 1 drama in 18-49. And holding steady at 10 was ”Private Practice” (2.3/6 in 18-49, 6.6 million viewers overall), which placed second among the broadcasters.

NBC improved its nightly average week to week thanks to a 10 p.m. repeat of ”The Voice” (1.5/4 in 18-49, 3.5 million viewers overall) airing in place of ”The Firm,” which will move to Saturdays. Thursday’s opening hour remains soft for the net, which went with an hourlong episode of ”30 Rock” (1.6/4 in 18-49, 3.9 million viewers overall). Also, ”The Office” hit a season low at 9 (2.5/6 in 18-49, 5.2 million viewers overall) and ”Up All Night” continues to put up unspectacular numbers at 9:30 (1.8/4 in 18-49, 3.7 million viewers overall).

CW saw nice week-to-week gains in its core demos for ”The Vampire Diaries” (1.2/3 in 18-49, 3.0 million viewers overall) and ”The Secret Circle” (0.8/2 in 18-49, 1.8 million viewers overall). ”Vampire” surged about 20% in both adults 18-34 (1.2/4) and women 18-34 (1.7/5) and edged out ABC and NBC in the 8 o’clock hour among persons 12-34 (1.3/4). And ”Secret” grew in both adults 18-34 (0.7/2) and women 18-34 (1.7/5).

Preliminary 18-49 averages for the night: Fox, 4.0/11; CBS, 3.6/10; ABC, 2.6/7; NBC, 1.7/5; Univision, 1.4/4; CW, 1.0/3.

In total viewers: CBS, 14.3 million; Fox, 12.2 million; ABC, 7.3 million; NBC, 3.9 million; Univision, 3.7 million; CW, 2.4 million.