NEW YORK -- Some of ESPN's 30 for 30 documentaries focus on well-known subjects worth revisiting. Others tackle relatively obscure topics that demand an in-depth look. But "Mike and the Mad Dog," which premiered at the Tribeca Film Festival on Friday night and airs on ESPN July 13, is sort of both of those at once. To sports fans in New York, Mike Francesa and Chris "Mad Dog" Russo are not just local celebrities, but broadcasting legends. However, the influence and importance of the WFAN show they co-hosted for 19 years is likely lost on sports fans elsewhere -- even with ones familiar with their names.

Indeed, the show's popularity -- and especially the late-career obsession with Francesa, and all the inside jokes that go along with it -- can be difficult to describe to the uninitiated. Trust me on this, as a guy who's tried and failed to explain the significance of this image to his wife:

"Mike and the Mad Dog," the documentary, does a fine job establishing why "Mike and the Mad Dog," the radio show, mattered so much, and why it resonated with New Yorkers. It makes the case that part of the reason the show worked was that, unlike many early WFAN hosts, they were New York guys (Long Island, to be exact) who had opinions about New York teams, and who actually sounded like their listeners. (Well, at least Francesa did; no human ever has sounded quite like Russo -- and certainly not the imitators whose shows launched after "Mike and the Mad Dog" became a hit.)

Ratings soared as the pair developed a remarkable chemistry -- an especially impressive achievement considering how much they fought being paired up in the first place. This isn't to say it was 19 years of paradise; the film touches on their assorted arguments, grudges and jealousies, my favorite of which is the time Francesa got mad at Russo for taking Francesa's name out of the show's jingle when he hosted solo while Mike was on vacation.

Francesa and Russo had a finger on the pulse of the New York fan, and the film shows how their passion connected with the city's blue-collar and white-collar listeners alike. There's a little archival moment in the documentary that I love, where they hold up one of the New York tabloids and criticize it for putting the Jets on the back page when something else apparently deserved the placement. They prided themselves on knowing what mattered to the New York fan, and perhaps more than anyone else in the local media, they could drive the conversation. (Huge props, by the way, to Michael Kay, now a rival radio host who has beefed with Francesa and been mocked by his fans, for appearing in the film to talk about the show's place in the city's sports mediascape.)

The show's influence is discussed in the film in two different ways: Outside of New York, it helped lead to an explosion of sports-talk radio during the 1990s. But Francesa and Russo also knew that, in New York, the GMs and decision-makers of the local teams were listening (or, at least, would find out what they said). Brian Cashman appears in the film; so does Giants co-owner John Mara, who says his father, late owner Wellington Mara, would listen to the show in the car. The movie even gets into the role the show played in bringing Mike Piazza to the Mets.

And so the film is a great nostalgia trip for those familiar with the show, and a good history lesson for those who aren't. It pretty thoroughly covers the show's origins, its success, and its ultimate end in 2008. (And yes, it also briefly touches on the allegations, investigated in this Deadspin post, that the duo questioned the loyalties of American Jews in the aftermath of 9/11.)

But what the film barely acknowledges is the show's weird afterlife -- the one that's led to four FrancesaCons, a Radio City reunion show, and the online community of millennials that's popped up around Francesa's solo show. The film is bookended with footage from FrancesaCon 2016 -- but the origins of the event or the community that led to it aren't really explained. Viewers will see the attendees and their inside-joke costumes, but won't necessarily understand what any of it means. (If you're wondering, the Diet Coke Pope, pictured above, is indeed in the film.)

Presumably, that's because that online following is more Francesa-centric, and didn't really start until after the duo split up. (And also because there's only so much you can squeeze into a 50-minute film.) But Francesa's embrace of that community has become a not-insignificant part of his story, and the whole thing has helped revive interest in the pair, and in their body of work together. If you're not YouTubing old clips after watching this film, something is wrong.

Near the end of the film, Jim Nantz mentions how fans of the show still hold out hope that Francesa and Russo may one day reunite. When he said this, the audience at the premiere in Tribeca applauded. The idea's been raised before; at the Radio City reunion last year, Francesa told the crowd to "never say never." And earlier this week, Russo told SI.com that he "would not rule it out."

When asked about it onstage by Andrea Joyce after the screening on Friday night, Francesa, who says he's leaving WFAN when his contract expires in December, said he was open to it:

"I think it's possible. I really do ... I don't know what I'm going to do. I want to do something. And I have to admit, the other day, [Russo] did this thing where he talked about it, where he did this interview. And it's been brought up a lot since Radio City, and to be honest with you, I don't know what's going to happen, in all seriousness. But would I listen if something was brought up about Mike and the Mad Dog, or Mike and the Mad Dog 2.0? Yeah, why not? I think it would be fun. I really do."

(Russo seemed caught off guard by the remarks. "That's the first time I've ever heard him say that," he said.)

During that Q&A, Joyce also asked Francesa and Russo what they missed most about doing the show together. "I miss the idea that I don't have a guy sometimes on the air who can challenge me and keep up with me from a sports standpoint," said Russo. He explained that he missed working with someone who "whatever you say, he might know as much as you do, if not more."

Francesa, meanwhile, told the audience that he misses how when the show really got going, "the note that we could reach, the thing that we could reach together, isn't the best that we could do. It's the best, I think, that anybody's ever done in sports. I don't think there's ever been anybody close." A brag for the ages, perhaps. But the film that had just ended made a pretty good case that he's exactly right.