PBS flexed its usual strength when the News and Documentary Emmy nominations were announced Thursday, racking up 37 nods. The public television system was followed closely by CBS, which had a particularly good showing, scoring 31 nominations, including 16 for its long-running Sunday newsmagazine “60 Minutes.” HBO placed third with 20 nominations, one of its largest hauls ever, followed by National Geographic, which earned 19. NBC had 17 and ABC got 9. TVNewser: David Letterman extortionist Joe Halderman was among those nominated for the 31st News and Documentary Emmy Awards. Halderman is nominated as a producer for the CBS 48 Hours Mystery story “American Girl, Italian Nightmare,” which is up for the Outstanding Continuing Coverage of a News Story in a News Magazine category Emmy. Halderman is currently serving a 6-month jail sentence.