Premiums receivable include premiums billed and in the course of collection as well as WBNR. WBNR is the component of premiums receivable that is subject to judgment and uncertainty. Premiums receivable as of December 31, 2009 was $269.9 million and included $221.1 million of WBNR that is based upon estimates. We evaluate the appropriateness of WBNR in light of the actual premium reported by the ceding companies. Any adjustments to WBNR that represent premiums earned are accounted for as changes in estimates and are reflected in results of operations in the period in which they are made.
We analyze historical loss development patterns and may adjust them for observed anomalies. For example, we observed that loss development patterns were much slower in Underwriting Years that were characterized by especially intense competition, known as the “soft market,” particularly in the North American excess-of-loss claims made class. We believe this is due to multiple year policies written by ceding companies and the deterioration in underwriting standards during these periods. In determining our loss development patterns for certain classes, we may exclude certain historical data from the soft market years because none of our business was written in these soft market periods. However, one of the risks of excluding some of the years is that we could be obscuring trends in loss development patterns. Our actuaries consider this when determining the credibility of indications that use these patterns. For a small number of reinsurance contracts, appropriate historical loss development patterns must be developed from ceding company data or other sources.
Year Ended December 31, 2009 as Compared with the Year Ended December 31, 2008
Net investment income was $163.9 million and $186.6 million for the years ended December 31, 2009 and 2008, respectively. Net investment income decreased in 2009 as compared with 2008 primarily due to a decrease in yields on invested assets and cash and cash equivalents. Net investment income decreased by $4.2 million and $1.3 million in 2009 and 2008, respectively, for adjustments related to our U.S. Treasury Inflation-Protected Securities (“TIPS”), reflecting changes in the consumer price index.
Operating expenses were $94.7 million and $88.2 million for the years ended December 31, 2009 and 2008, respectively. Operating expenses include $64.4 million and $63.7 million for 2009 and 2008, respectively, relating to other underwriting expenses. The remaining $30.3 million and $24.5 million in 2009 and 2008, respectively, related to costs such as compensation and other corporate expenses associated with operating as a publicly-traded company. The increase in operating expenses was primarily attributable to an increase in performance-based compensation accruals in 2009, partially offset by a decrease of $4.3 million in expenses related to entering into the agreement with Topiary in 2008.
Platinum Holdings is a holding company, the assets of which consist primarily of shares of its subsidiaries. Platinum Holdings depends primarily on its available cash resources and liquid investments, and dividends, interest and other distributions from its subsidiaries, to meet its obligations. Such obligations may include operating expenses, debt service obligations, dividends on its common shares and repurchases of common shares or other securities. Applicable laws and statutory requirements of the jurisdictions in which our regulated reinsurance subsidiaries operate, including Bermuda and the United States, limit the payment of dividends and other distributions from these subsidiaries. Based on the regulatory restrictions of the applicable jurisdictions, we estimate the maximum amount available for payment of dividends or other distributions by our reinsurance subsidiaries without prior regulatory approval in 2010 to be $431.0 million. The ability of our reinsurance subsidiaries to pay dividends is also constrained by our dependence on the financial strength ratings by A.M. Best and S&P of our reinsurance subsidiaries, which depend to a large extent on the capitalization levels of the reinsurance subsidiaries. We believe that Platinum Holdings has sufficient cash resources and its subsidiaries have available dividend capacity to service our current outstanding obligations. Platinum Holdings received dividends from its subsidiaries of $255.0 million during the year ended December 31, 2009.
On a consolidated basis, our aggregate cash and invested assets totaled $4.4 billion and $4.3 billion at December 31, 2009 and 2008, respectively. Additionally, we had net balances due from brokers related to the sale of securities of $123.3 million and $20.3 million at December 31, 2009 and December 31, 2008, respectively, which are included in other assets and other liabilities. Our investment portfolio consists primarily of diversified, high quality, predominantly publicly-traded fixed maturity securities. The investment portfolio, excluding cash and cash equivalents and short term investments, had a duration of 4.3 years and 3.2 years as of December 31, 2009 and 2008, respectively.