Thank you, Jay. At quarter-end, our servicing-related investments, comprised solely of full MSRs, represented approximately 26% of our equity capital and approximately 6% of our investable assets, excluding cash. Our aggregate investment portfolio composition is shown on Slide 5.
Servicing-related assets as a percentage of equity increased to 26% from 20% due to the additional deployment of cash into select MSR investments during the quarter. As a result, our RMBS portfolio accounted for approximately 68% of our equity and approximately 94% of our investable assets, excluding cash at quarter-end.
As of December 31, we held MSRs with a UPB of $11.7 billion and a market value of approximately $122.8 million, as shown on Slide 6. The total MSR portfolio prepayment speeds continued to decline during the quarter, despite a pickup in delinquencies due to hurricane-related impacts.
Life-to-date, our conventional MSR CPRs have averaged approximately 10.1%, while our government MSRs CPRs averaged approximately 10.4%.
As of December 31, the RMBS portfolio stood at approximately $1.9 billion, as shown on Slide 7. Opportunistically, we expect to redeploy a portion of the RMBS funds into MSRs.
At quarter-end, the 30-year securities position of our RMBS portfolio stood at 73%, while the 20-year and 15-year fixed-rate pools, as well as shorter-duration assets, represented the balance of the RMBS portfolio.
In the fourth quarter, the RMBS portfolio posted a weighted average 3-month CPR of approximately 6.45%, up from 5.95% posted in the previous quarter, as shown on Slide 8.
Overall, the portfolio continued to benefit from its collateral composition and continued to vest Fannie Mae aggregate prepayment speeds during the quarter.
For the fourth quarter, we posted a 1.27% RMBS NIM versus 1.26% for the third quarter. The slim increase in NIM was driven by the portfolio of collateral composition and reduced swap costs, which helped offset increased repo costs.
At quarter-end, repo cost averaged 147 basis points versus 137 basis points in the third quarter. The higher costs were partially offset by increased 3-month LIBOR, which benefited the receiving portion of our swap hedges. The received portion of our swap hedges rose to 144 basis points versus 131 basis points posted in the third quarter due to LIBOR resets. In the near term, we expect our NIM to fluctuate on increased repo cost.
During the quarter, the aggregate portfolio operated with leverage of 5.3x in a negative duration gap. As shown on Slide 9, we ended the quarter with an aggregate portfolio duration gap of minus 0.91 years.
During the first quarter of 2018, we've proactively managed our hedges, as asset durations have extended in the portfolio due to rising interest rates. We have increased our swap hedge ratio as well as added additional swaptions and treasury feature hedges to the portfolio. We expect to continue to evaluate and alter the portfolio as the year progresses.
I'll now turn the call over to Marty for our fourth quarter financial discussion.