Washington-based consulting firm Callahan & Associates estimated nonbanks originated 47% of mortgages in 2015, compared with 45% for banks and 8% for credit unions. As banks' share fell from 74% in 2007 to 52% in 2014, nonbanks' share rose from 23% to 43% and credit unions from 3% to 5%.

Growth continued for credit unions into the first quarter of 2016. They originated $26.7 billion in mortgages, which accounted for 7.6% of the $350 billion market.

"Credit unions have been increasing their portion of the mortgage pie over the last 10 years. If you look at the trend, it continues to be very positive, with credit union market share up from 2% in 2006," Sam Taft, director of industry analysis for Callahan & Associates, said.

Yet the fastest advances have been made by nonbanks, which originate loans and sell them to investors. Some also service the loans. Nonbanks have invested heavily in online technology that allows consumers to apply swiftly and easily for loans and invisibly threads through a maze of regulations and internal lending rules.

Quicken Loans Rocket Mortgage Product Lead Regis Hadiaris said many consumers can't, or simply don't want to, navigate the mortgage process within brick-and-mortar lenders' limited hours.

"A growing number of them have the expectation that they can do anything online at any time, whether that's shop, book a trip or even see a doctor. Rocket Mortgage meets this expectation," Hadiaris said. "Two-thirds of Rocket Mortgage users are looking to buy a home, and of those, 72% are first-time buyers. This is direct proof that homebuyers, many of whom are millennials, are embracing the online process."

To reach the large number of consumers needed to pay for their technology investments, nonbanks must advertise heavily.

Quicken Loans aired its first Super Bowl ad during last winter's game featuring Rocket Mortgages' "Push Button. Get Mortgage" slogan. Now it is airing ads tied to Star Trek Beyond, which opened in theaters July 22. The ads show a Vulcan couple using and approving of the Quicken Loans tool. Jay Farner, Quicken Loans' president/chief marketing officer, said Rocket Mortgages was "a perfect fit with the high-tech Star Trek universe."

loanDepot's 2015 prospectus showed the company spent $96 million on advertising in 2014, compared to $54 million in direct origination expenses.

"We intend to continue to dedicate significant resources to our marketing and brand advertising efforts and strategic relationships," the prospectus said. "We utilize highly targeted and sophisticated marketing strategies, which include internet, broadcast and new media, strategic alliances and a national television campaign to build brand awareness. Our operating results and ability to sustain and grow loan volume will depend, in part, on our ability to continue to make effective investments in marketing and product development."

Consider this: Navy Federal Credit Union, the world's largest credit union, has more than 13,000 employees, with more than one-third employed in its 278 branches. One-third of its employee and office costs in 2015 was $511 million.

loanDepot, one of the fastest-growing nonbank lenders, had 4,126 full-time equivalent employees in 2015.

"Our hybrid originate-to-sell and marketplace business model allows us to generate significant loan volume with less capital than traditional market participants," the prospectus continued. "For the 12 months ending June 30, 2015, we originated $22.1 billion in loans, representing 125% year-over-year growth. Moreover, we have generated this substantial growth while maintaining profitability since 2012."

Quicken Loans originated $80 billion in mortgages last year and is on track to match or beat that number this year, spokesman Jordan Fylonenko said. Its mortgage originations were up from $60 billion in 2014.

CUNA Senior Economist Perc Pineda said banks have been trying to use technology to shorten closing times for decades. In 1995, banks set a goal of reducing underwriting times from 12.5 hours to 15 minutes.

"There are credit unions that use technology, but it is not as high as the banking and nonbanking sectors," Pineda said.

Credit unions emphasize service to members through relationships built over years.

"Credit unions are very conservative in where they can cut costs," Pineda said. "What makes a credit union stand out is service, that you know your members more than anyone else."

Mortgage Bankers Association Chief Economist Mike Fratantoni said while technology is improving the consumer experience, he isn't sure if it's reducing costs.

"The next couple of years should be very interesting along that line, but I don't see much of an impact yet," Fratantoni said. "We're at the beginning stages."

Taft said an institution's use of technology as a complement to its branch operations will only grow in importance. In the end, he said he believes credit unions won't be left behind by nonbanks' technology advances.

"Credit unions are well positioned to adapt to the growing changes in the real estate lending market, and are actively investing in the required infrastructure to stay competitive," he said.

Meanwhile, Taft said, credit unions retain the advantage of deep ties to members.

"Credit unions' ability to listen to their members and their stories in an effort to write more and better mortgages will also continue to be important," he said. "We hear lots of stories about members getting declined by big banks and financial institutions because someone doesn't fit in the 'box' on their application. Credit unions are much more willing to take a second look at these applications and try to talk to the member and get comfortable writing the loan."

Banks' falling share of mortgage originations in part reflects a strategic retreat from a market that many considered too risky, Fratantoni said.

"You've seen many banks pull back from their involvement in the mortgage market," he said. "Independents and nonbanks are really filling the void because that's the only business they're in, even though it has become more expensive and heavily regulated. It's still a challenge to get everything right, and the cost of getting it wrong is still pretty high."

In a February column in National Mortgage News, Christopher Whalen, a senior managing director at Kroll Bond Rating Agency, said banks are pining for the heady days of 2004 and 2005 when banks sold their bundles of subprime loans into a robust private market with less regulation and oversight.

"The largest banks, in particular, have been receiving a continuous battering by regulators and prosecutors reinforcing the message that banks need to avoid financial and reputational hazards, particularly in areas such as residential mortgage loans," Whalen said. "As the veteran chief executive officer of one century-old mortgage lender told us last year, 'the consumer has become toxic.' Not surprisingly, that banker has made growing commercial lending his new priority."

loanDepot withdrew its plans for an initial public offering in November 2015 because the expected share price was not meeting expectations, but it has not slowed its growth. In a recent interview, loanDepot CFO Bryan Sullivan said the company is built for tackling complexity, and the banks' retrenchment has given his company more room to expand.

"We're trying to do it from both ends where banks are pulling back and where smaller players are struggling to compete," Sullivan said. "We started from zero and we have 2% of the market. It's still highly fragmented so there is opportunity for us to take share from banks but also from smaller competitors as the home loan space becomes excessively complex. We have the scale to do that."

In the 1990s, Quicken Loans began building a centralized platform that now allows it to seamlessly lend in all 50 states and serve consumers from their beginning conversation through servicing for the life of the loan, Hadiaris said.

"This approach … has driven our exponential growth and allows us to quickly adapt to ever-shifting regulations," he said. "Lenders who don't implement technology as the driving force in their business will be left behind in today's evolving market and regulatory environment."