Platinum Holdings and Platinum Bermuda lease office space in Pembroke, Bermuda, where our principal executive office is located. Platinum US and PASI lease office space in New York, New York. In addition, Platinum US leases office space in Chicago, Illinois and PASI leases office space in Stamford, Connecticut. We renew and enter into new leases in the ordinary course of business and anticipate no difficulty in extending our leases or obtaining comparable office facilities in suitable locations. We consider our facilities to be adequate for our current needs.
Unpaid losses and LAE are estimates of future amounts required to pay losses and LAE for claims under our assumed reinsurance contracts that have occurred at or before the balance sheet date. Unpaid losses and LAE are estimated based upon information received from ceding companies regarding our liability for unpaid losses and LAE, supplemented by our estimates of losses and LAE for which ceding company reports have not been received, our historical experience for unreported claims and industry experience for unreported claims. Unpaid losses and LAE include estimates of the cost of claims that were reported, but not yet paid, and IBNR. In addition, we estimate our ULAE reserves based on our administrative costs of managing claims.
In property classes, there can be additional uncertainty in loss estimation of large catastrophe events. With wind events, such as hurricanes, the damage assessment process may take more than a year. The cost of rebuilding may increase due to various factors including shortages for construction materials and labor. In the case of earthquakes, the damage assessment process may take several years to discover structural weaknesses not initially detected in buildings. The uncertainty inherent in loss estimation is particularly pronounced for casualty classes, such as umbrella liability, general and product liability, professional liability and automobile liability, where information, such as required medical treatment and costs for bodily injury claims, emerges over time. In the overall loss estimation process, provisions for economic inflation and changes in the social and legal environment are considered.
Net losses from current year major catastrophes were $26.1 million and $68.9 million for the years ended December 31, 2013 and 2012, respectively. Net losses from 2012 major catastrophes for the year ended December 31, 2012 were attributable to Hurricane Sandy, PCS Catastrophes 66 and 67, tornado and hailstorm events, primarily in Kentucky and Tennessee, PCS Catastrophe 74, severe weather, including a tornado and hailstorm event in the U.S. Midwest, PCS Catastrophe 83, a U.S. multi-day straight line wind and thunderstorm event and Hurricane Isaac.
2014 versus 2013: Net losses and LAE increased by $35.4 million for the year ended December 31, 2014 as compared with the year ended December 31, 2013. The increase in net losses and LAE was primarily due to a decrease in net favorable loss development, an increase in losses from catastrophe losses from non-major events and an underwriting loss in our North American crop class as compared with underwriting income in our North American crop class in the same period in 2013. This was partially offset by a decrease in net losses from current year major catastrophes.
2013 versus 2012: The Casualty segment calendar year losses, excluding prior years' loss development, were $219.1 million and $225.8 million for the years ended December 31, 2013 and 2012, respectively. The calendar year loss ratios, excluding prior years' loss development, were 73.5% and 77.4% for the years ended December 31, 2013 and 2012, respectively. The decrease in calendar year losses and the related loss ratios, excluding prior years' loss development, was primarily due to lower initial expected loss ratio estimates in the current year for several North American casualty classes as we lowered our estimates as a result of better than expected historical loss experience. Also, there was a lower loss ratio in the financial lines class in 2013 as compared with 2012. Calendar year losses and related loss ratios, excluding prior years' loss development, were also impacted by changes in the mix of business.
2013 versus 2012: Net investment income was $72.0 million and $99.9 million for the years ended December 31, 2013 and 2012, respectively. Net investment income decreased during the year ended December 31, 2013 as compared with 2012 primarily from a decrease in the average book yield for the portfolio of total investments and cash and cash equivalents from 2.6% to 2.0%. The change in the average book yield reflects purchases, sales, maturities and paydowns. Contributing to the decrease in investment income was a reduction of approximately $324.6 million in the average book value of our investments and cash and cash equivalents for the year ended December 31, 2013 as compared with 2012, primarily due to share repurchases, dividend payments and negative operating cash flows.
During the year ended December 31, 2014, dividends of $339.0 million were paid by the reinsurance subsidiaries of Platinum Holdings, of which $264.0 million was paid by Platinum Bermuda to Platinum Holdings and $75.0 million was paid by Platinum US to Platinum Finance.
See Note 1 to the "Consolidated Financial Statements" contained elsewhere in this Form 10-K for a discussion of recently issued accounting standards. As of December 31, 2014, there were no recently issued accounting standards applicable to the Company.