Although not a financial measure, management's decisions are also greatly influenced by access to specialized underwriting and claims expertise in our lines of business. We have chosen to operate in specialty niches with certain common characteristics which we believe provide us with the opportunity to use our technical underwriting expertise in order to realize underwriting profit. As a result, we have focused on underserved markets for businesses characterized by higher severity and low frequency of loss where we believe our intellectual capital and financial strength bring meaningful value. In contrast, we have avoided niches that we believe have a high frequency of loss activity and/or are subject to a high level of regulatory coverage requirements, such as workers compensation and personal automobile insurance, because we do not believe our technical expertise is of as much value in these types of businesses. Examples of niches that have the characteristics we look for include bluewater hull which provides coverage for physical damage to, for example, highly valued cruise ships, and directors and officers liability ("D&O") insurance which covers litigation exposure of a corporation's directors and officers. These types of exposures require substantial technical expertise. We attempt to mitigate the financial impact of severe claims on our results by conservative and detailed underwriting, prudent use of reinsurance and a balanced portfolio of risks.
Included in the 2004 incurred losses for specialty business was a series of claims aggregating approximately $2 million, from a single 2002 underwriting year policy that were all below the $150,000 attachment point of our 2002 year reinsurance program. Such unusual loss activity was the primary reason for the $2.3 million of net prior years' loss deficiencies recorded in 2004 for specialty business.
The 2004 underwriting results benefited from improved market conditions since 2002 across all lines of business as reflected in the 93.2% combined ratio. The 2004 underwriting results were negatively impacted by approximately $2.8 million or 1.2 loss ratio points for net prior year loss development of which $4.8 million was for marine business, $2.3 million for specialty business and $0.7 million for runoff business, offset by $2.8 million of prior year savings for professional liability business and $2.2 million from business assumed from our Lloyd's operations. The net loss to the Insurance Companies from Hurricane Ivan of approximately $3.1 million increased the 2004 marine combined ratio by 3.7 ratio points and the Insurance Companies' combined ratio by 1.3 ratio points.
Following are the results of operations of the Lloyd's Operations for each of the years in the three-year period ended December 31, 2006:
The 2005 underwriting results were favorably impacted by approximately $1.2 million or 1.1 loss ratio points for net prior years' savings.
The table below illustrates the Company's participation for each year of account in Syndicate 1221:
Investments and cash increased to $1,475.9 million at December 31, 2006 from $1,182.2 million at December 31, 2005 and $854.9 million at December 31, 2004. The increases were primarily due to the positive cash flow, $123.5 million of net proceeds from the 7% Senior Notes offering completed in April 2006 and $123.8 million of net proceeds received from the equity offering in October 2005. Net investment income was $56.9 million for 2006, $37.1 million for 2005 and $26.8 million for 2004.
We primarily rely upon dividends from our subsidiaries to meet our holding company obligations. Since the issuance of the senior debt in April 2006, the holding company cash obligations primarily consist of semi-annual interest payments of $4.4 million. Going forward, the interest payments will be made from a combination of funds at the Parent Company and dividends from its subsidiaries. The dividends have historically been paid by Navigators Insurance Company. At December 31, 2006, the approximate maximum amount available for the payment of dividends by Navigators Insurance Company during 2007 without prior regulatory approval was $52.4 million. No dividends were paid by Navigators Insurance Company during 2006. During 2005 and 2004, Navigators Insurance Company paid dividends to the Company of $3 million and $6 million, respectively.