Season eleven, however, suffered a steep drop in ratings, a drop attributed by some to the arrival of new shows such as The Voice and The X-Factor. The ratings for the first two episodes of season eleven fell 16–21% in overall viewer numbers and 24–27% in the 18/49 demo, while the season finale fell 27% in total viewer number and 30% in the 18-49 demo. The average viewership for the season fell below 20 million viewers the first time since 2003, a drop of 23% in total viewers and 30% in the 18/49 demo. For the first time in eight years, American Idol lost the leading position in both the total viewers number and the 18/49 demo, coming in second to NBC Sunday Night Football, although the strengths of Idol in its second year in the Wednesday-Thursday primetime slots helped Fox achieve the longest period of 18-49 demographic victory in the Nielsen ratings, standing at 8 straight years from 2004 to 2012.
How long did Fox reign in the 18-49 demographics in the Nielsen ratings?
eight years