The bank reaps expanding yield as maturing lower-yielding securities roll into higher market rates, supporting net interest margin (NIM, the percentage difference between interest earned on assets and paid on liabilities). This recurring cash flow reinvestment generates steady top-line growth without taking on extra duration risk. In the third quarter, portfolio runoff was $770 million at an average yield of approximately 3.3%. Those cash flows were reinvested at an average yield slightly over 5.1%, represe ...