The New Yorker, the beloved weekly magazine encompassing journalism, fiction, poetry and cartoons, is celebrating its one-hundredth birthday. “Sunday Morning” contributor (and New Yorker writer) Kelefa Sanneh goes inside the magazine’s history with editor David Remnick, manager Bruce Diones, and Fergus McIntosh, who leads the magazine’s battalion of fact-checkers, to discuss The New Yorker’s longevity, national reach, and idiosyncratic appeal.