NEW YORK — CBS strengthened its dominance over the television industry this year at the same time that the unprecedented reign of "American Idol" came to a close.
The traditional television season ended Wednesday. Though that marker is losing its meaning with more fresh programming airing during the summer, it's still a good time to take stock on where the industry stands.
For the 10th time in 11 years, CBS was the nation's most-watched network, the Nielsen company said Thursday. CBS' margin of victory was wider than any other network in 24 years and it won among 18-to-49-year-old viewers, a group coveted by advertisers, for the first time in 21 years.
In prime time through May 19, CBS averaged 11.85 million viewers this season. ABC was its closest competitor, at a full 3 million viewers behind. Fox finished third and NBC was fourth, Nielsen said.
The "American Idol" streak of nine years as the nation's most popular television entertainment program ended this season. Its popularity had been sliding for the past few years — typical of most shows that have been on for a long time — but accelerated this year with a cast of judges that didn't click and the emergence of NBC's "The Voice" as a strong alternative.
No other show in television history has come close to such sustained dominance. Three other programs have had four-year reigns as the top program in household ratings: the comedy "I Love Lucy" in the 1950s, the western "Gunsmoke" heading into the 1960s and "The Bill Cosby Show" in the 1980s, Nielsen said.
The new No. 1 show depends on how you look at the ratings.
NBC's "Sunday Night Football" telecast is technically the narrow winner, but many in TV say that a live sports telecast should not count in the rankings. The Tuesday night CBS drama "NCIS" is the top program otherwise, its first win.
TV's top comedy is "The Big Bang Theory" on CBS, averaging 15.6 million viewers per week. That's up from 9.4 million viewers during the 2008-09 season, a testament to how the show has grown in popularity with the help of reruns that air frequently on TBS and elsewhere.
The weakness of "American Idol" was the biggest factor in Fox's viewership dropping 20 percent from last season. Both ABC and NBC were down 6 percent, with ABC's drop slightly steeper among the youthful viewers that both networks aim for. CBS was up 1 percent, its ratings helped because this was the year it telecast the Super Bowl.
CBS officials said they still would have won among 18-to-49-year-old viewers even with the Super Bowl counted out. That's a particular point of pride for the network because their rivals often deride them for having the oldest audience in network TV.
CBS Corp. CEO Leslie Moonves had plenty to crow about last week when he appeared before advertisers to introduce the network's fall schedule.
"No matter how many times I tell our success story, I never get tired of it," Moonves said. "It just gets better and better."
The network's success breeds stability — 20 series were renewed for next season — and means only the very best of the new shows that it develops can find room on the schedule.
That will make CBS hard to beat in the next few years, said Brad Adgate, an analyst for Horizon Media. To unseat the network, CBS would have to see its schedule falter and a rival will need some unusually fruitful years in development, like when ABC introduced "Lost," ''Desperate Housewives" and "Grey's Anatomy" in the same year.
"I don't see it happening in the foreseeable future," Adgate said.