Remember when you refinanced your house in order to take a vacation or spend more at the mall? Well, refinancing these days also involves borrowers paying down their mortgage principal. From Housing Wire:

"Interest rates on fixed-rate mortgages are at 50-year lows, making refinancing attractive if borrowers qualify," [said Freddie Mac Chief Economist Frank Nothaft]. "Similar rates on savings instruments like CDs are also very low, which makes the choice of paying down mortgage principal very attractive to borrowers with extra cash reserves."