It's usually a good year in Detroit's real estate market when one home sells for $1 million or more.

Detroit is now concluding its most remarkable sales year in decades for upscale listings: Four mansions and one penthouse condominium within the city limits all sold for $1 million or more in 2017.

Three of the sales were in the historic Boston-Edison neighborhood, which, until this year, had never seen a house break the $1-million mark. The reported $2.7-million sale of the massive Bishop's Mansion in Palmer Woods set an all-time price record for any single-family home in the city, according to local agents.

And agents say that many of these $1 million-plus property buyers intend to live in their new Detroit home — not simply flip it.

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This year's mansion boom shows how property values in the most desirable neighborhoods have been rising fast amid the strengthened economy and growing perception of Detroit as a city on the rebound. Less than a decade ago, some of these same mansions sold for a fraction of what they recently fetched.

"It was extraordinary to have this happen to so many houses in one year," said Realtor Betty Warmack of Real Estate One, who has been selling houses in Detroit for more than 30 years. "When I talk to other agents, we all see the values climbing. And it's pretty exciting to see that. It seems to be across the board."

Even with recent price gains, Detroit is still a market where buyers can get big bargains on big houses that would cost a lot more if located outside city limits.

A prime example is the Motown Mansion, the 100-year-old Boston-Edison estate once own by record label founder Berry Gordy. The home sold for $1.65 million in August to a San Francisco couple.

"If the Motown Mansion had been in, say, Birmingham, it would have been a $10 million property for sure," said Realtor Deborah Smith of Keller Williams Realty, who represented the mansion's seller.

Coming from San Francisco's uber-expensive real estate market, Alan Brown, the new owner of the Motown Mansion, was astounded by how far money can stretch in Detroit.

"If you look at the history of Detroit real estate, these are astronomical prices. But if you look at any other market in the United States, these are steals," said Brown, a management consultant in the nonprofit arts sector who grew up in Birmingham and is a University of Michigan graduate. "I've had people tell me that in another city, this would be a $10-million or $20 million house."

By coincidence, he and his partner, Aldo Torres, sold their house in San Francisco for the same $1.65-million price that they paid for the 2.2-acre Motown Mansion. The San Francisco house was 1,800 square feet. The Motown Mansion estate, in comparison, has nearly 17,000 square feet between its main house, pool house and carriage house.

"Some people would have looked at that price and been 'Oh my God, that's so expensive,' " Brown said. "I looked at that price and went 'Oh, wow, I could get the Motown Mansion for the same price that I sold my little Victorian in San Francisco.'"

They hope to someday uncover and restore the mansion's indoor swimming pool, where, as legend has it, a young Michael Jackson learned how to swim. They're currently seeking a mechanic to fix the vintage Brunswick pin machine in the mansion's bowling alley.

"This is my forever home. I never want to buy another house in my life," he said.

The other four big sales this year were:

The Charles T. Fisher mansion in Boston-Edison, which sold for $1.25 million in April.

A 2,500-square-foot penthouse in downtown's Westin Book Cadillac, which sold for $1.79 million in June.

The Walter Briggs mansion in Boston-Edison, which sold for $1.03 million in September.

The 35,000-square-foot Bishop Gallagher mansion in Palmer Woods, which sold for a reported $2.7 million in October.

Still a bargain

Of course, $1 million-plus house sales are still a rarity for Detroit. The median home sale price in the city was $28,000 in November, well below the overall Wayne County median of $123,000, according to the Realcomp listing service, which doesn't include private sales or for-sale-by-owner transactions.

The median home sale price in San Francisco was $1.24 million in October, according to the Zillow real estate website.

Still, Detroit prices are on the rise.

Real estate agent Steven Edward of Detroit-based Downtown Realty said that two years ago, a typical three-bedroom house that is just outside one of the city's more affluent neighborhoods sold for about $25,000. Today, those houses go for $35,000 to $40,000, he said.

"Ninety percent of the clients that I deal with are overseas investors. And with all these investors coming in, they are driving the prices up," Edward said. "And everything that Mayor (Mike) Duggan is doing, as far as the investments in the neighborhoods, that is driving the values of the homes up as well.”

3 in Boston-Edison

Boston-Edison saw its first $1-million sale this spring when actor Hill Harper, who stars in ABC's "The Good Doctor" and previously played a coroner in "CSI: New York," bought the Charles T. Fisher mansion, the neighborhood's largest house.

The 18,000-square-foot mansion (including carriage house) dates to 1922 and features 14 bedrooms, 14 bathrooms and a private office that reportedly once connected Charles Fisher to the former General Motors headquarters in New Center.

Fisher was an automotive pioneer who co-founded Fisher Body Co. with a brother and uncle, later becoming a GM executive. A cousin, Michael Fisher, bought the mansion out of foreclosure in 2008 for $625,000, property records show. This year Harper paid $1.25 million for the house — its full asking price.

For Warmack, the seller's agent, it marked the second time in her 31-year career that she sold a Detroit house for $1 million or more. Her first such sale happened about a decade ago with a $1-million listing in the gated Shorepointe Village at Grayhaven neighborhood on the east riverfront.

Warmack noted how all of this year's $1 million-plus house sales occurred in neighborhoods that are zoned for single-family homes and cannot be subdivided into rentals.

"A lot of people, when they see the size of these homes, they think of terms of AirBNBs, and that's not allowed," she said.

The Walter Briggs mansion, also known as Stone Hedge, was built in 1915 by Walter O. Briggs, who founded an auto supplier and owned the Detroit Tigers from 1920 until his death in 1952.

The house spans more than 9,500 square feet and has 11 bedrooms, nine bathrooms and nine fireplaces. The mantel in the library features carved-in faces of baseball greats Hank Greenberg, Babe Ruth, Charlie Gehringer and Lou Gehrig.

Back in 2012, the house sold for a bargain-basement $395,650.

But five years later and after more than $200,000 in renovations, the house listed for $1.050 million this year. It had four offers over asking price, according to Realtor Jason Hill of Historic Realty Detroit. The sale price — $1.035 million — reflected a discount following the home inspection.

Hill said he believes the momentum in Detroit's increasingly vibrant downtown is helping to boost prices in many of the city's neighborhoods.

"The sense that there is a real downtown has brought value to areas where we wouldn't see (such) value," Hill said. "I get calls from New York to Germany. People want to invest and be a part of it any way they can."

Even though many of the recent buyers see their high-end Detroit properties as investments that will appreciate in value, "for the most part, people are actually buying them to live in," he said.

Record-breaking condo

A price record for a Detroit condo was set in June when a penthouse on the 29th floor of downtown's Westin Book Cadillac, 1135 Shelby, sold for $1.795 million cash.

The 2,500-square-foot unit features 35-foot vaulted ceilings and 11 rooms, including three bedrooms, a dining room and a library. It is one of 62 residences in the Book Cadillac, which is also an upscale hotel.

The luxury condo previously went for about $725,000 in 2008.

The condo's broker, Kyle Swink of Coldwell Banker Weir Manuel, attributed the record-breaking sale to the Book Cadillac's desirable location in booming downtown as well as the penthouse's uniqueness.

There were at least two other $1-million-plus condos still sitting on the Detroit market this week: another Book-Cadillac penthouse for $1.75 million and a large $1.4-million loft near the east riverfront.

"There's definitely people from outside areas that see Detroit as an opportunity," Swink said. "Three to five years ago, I don't think there was a lot of confidence as to where the city was going."

The big house

This year's biggest transaction was the Bishop's Mansion, a 62-room house in Palmer Woods that is the largest private residence in Detroit. Built in 1926, the house was once owned by the Catholic Archdiocese of Detroit and home to Catholic Bishop Michael Gallagher.

The archdiocese sold the house in 1989 to the Detroit Pistons' John Salley. Six years later, Salley sold it to Great Faith Ministries International.

The ministries' Bishop Wayne T. Jackson used the house as both a residence and for church offices.

This October, the mansion sold to a California investor for a reported $2.7 million. It was the biggest sale price for a Detroit residence that agents can recall — perhaps the biggest ever.

The California investor owns several other historic Detroit properties, which he generally rents out, said his local agent, Antonio Rodriguez of Re/Max Suburban.

The six inspectors involved in vetting the home "basically said they’ve never seen anything like it," Rodriguez said, noting the house's detailed interiors, imported Italian marble pillars and wood paneling from Germany's Black Forest. "When they were done with the inspection, they said you couldn’t rebuild this house for $50 million."

Contact JC Reindl: 313-222-6631 or jcreindl@freepress.com. Follow him on Twitter @JCReindl.