Bank and thrift holdings of adjustable-rate mortgages have increased significantly in recent years, according to an analysis by Inside Mortgage Finance, driven in part by originations of jumbo mortgages. Banks and thrifts held $647.42 billion in ARMs in portfolio as of the end of 2013, according to call-report data. The total ARM portfolio increased by 0.7 percent last year, the third annual increase in a row, while the aggregate bank and thrift retained portfolio of first-lien mortgages fell 3.0 percent. ARMs accounted for 37.1 percent of the bank/thrift mortgage portfolio at the end of 2013, compared to just 31.9 percent at the end of 2011. Lenders have to keep generating...[Includes two data charts]