On balance, this means gross premiums were up 11% for the quarter and net premiums were up 8% for the quarter. Our third quarter underwriting results were very good in light of catastrophe activity which we would consider higher than normal for the quarter. Our total net catastrophe losses, net of reinstatements in the quarter were $91 million. In addition to these catastrophe losses, our underwriting results for the quarter absorbed a higher level of large property losses as a result of the cumulative impact of major and tragic weather disasters throughout the United States. US events for the year-to-date are estimated to exceed $35 billion in economic losses and are in addition to the highest insured earthquake losses in history.
Our prior year reserves continue to develop favorably and during the quarter we recorded a combined ratio of 91.5% which we believe is a very healthy result consider the prevailing overall adverse market conditions. Net investment income was under significant pressure in the quarter due to continued low interest rates and a reduction in the valuation of our alternatives portfolio driven by the extreme volatility in the global financial markets.