(CNN) — Few TV stars burned brighter than Mary Tyler Moore, whose association with two for-the-ages sitcoms burnished her Hall of Fame credentials. Her broader significance as a cultural icon is more open to debate, and receives a workout in “Being Mary Tyler Moore,” a dutiful HBO documentary devoted to her life and career that’s at its best when illustrating her comedic gifts.

Running two hours, the film has the luxury of taking some time to do just that, with a long section devoted to “The Mary Tyler Moore Show” in general and the “Chuckles the Clown” episode in particular, rightfully considered one of the best sitcom episodes ever.