Question: How long did the original broadcaster of the series in which Knight Fall was an episode reign in the 18-49 demographics of the Nielsen ratings?

<P0-S0> "House", also known as "House, M.D. <P0-S1> ", is an American medical drama series which premiered on Fox on November 16, 2004. <P0-S2> "House" was created by David Shore. <P0-S3> The show follows Dr. Gregory House (Hugh Laurie), an irascible, maverick medical genius who heads a team of diagnosticians at the fictional Princeton-Plainsboro Teaching Hospital (PPTH) in New Jersey. <P0-S4> In a typical episode, the team is presented with an unusual case; the storyline follows the diagnosis of the patient's illness, a process often complicated by the internal competition and personal foibles of the diagnostic team. <P0-S5> The team leader, House, frequently clashes with his boss (Dr. Lisa Cuddy (Lisa Edelstein) in seasons 1 through 7, and Dr. Eric Foreman in season 8), and his only friend, Dr. James Wilson (Robert Sean Leonard). <SEP> <P1-S0> "Knight Fall" is the eighteenth episode of the sixth season of the American medical drama "House" and it is the 127th episode overall. <P1-S1> It aired on April 19, 2010 and was directed by Juan J. Campanella. <SEP> <P2-S0> 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. <P2-S1> 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. <P2-S2> 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. <P2-S3> 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. <SEP> <P3-S0> the loss of viewers continued into season 12, which saw the show hitting a number of series low in the 18-49 demo. <P3-S1> the finale had 7.2 million fewer viewers than the previous season, and saw a drop of 44% in the 18-49 demo. <P3-S2> the season viewers averaged at 13.3 million, a drop of 24% from the previous season. <P3-S3> the thirteenth season suffered a huge decline in the 18–49 demographic, a drop of 28% from the twelfth season, and american idol lost its top 10 position in the nielsen ratings by the end of the 2013–14 television season for the first time since its entry to the rankings in 2003 as a result, although the entire series to date had not yet been dropped from the nielsen top 30 rankings since its inception in 2002. <SEP> <P4-S0> a second season of 18 episodes was confirmed, and production started in the fall of 2016 in toronto. <P4-S1> on march 27, 2017, ion television picked up the exclusive rights to broadcast the series in the united states, where it is presented as an original series for the network.