As a result of this transaction, we recorded approximately $98.9 million of written premium and approximately $31.6 million of fee income during the year ended December 31, 2013 related to CCPH since the date of acquisition.
We manage the assets of NGHC and its subsidiaries for an annual fee equal to 0.20% of the average aggregate value of the assets under management for the preceding quarter if the average aggregate value for the preceding quarter is $1 billion or less and 0.15% of the average aggregate value of the assets under management for the preceding quarter if the average aggregate value for that quarter is more than $1 billion. We managed approximately $0.8 billion of assets as of December 31, 2013 related to this agreement. As a result of this agreement, we earned approximately $1.7 million, $1.5 million and $1.6 million of investment management fees for the years ended December 31, 2013, 2012 and 2011, respectively.
Net Written Premium. Net written premium is gross written premium less that portion of premium that we cede to third party reinsurers under reinsurance agreements. The amount ceded under these reinsurance agreements is based on a contractual formula contained in the individual reinsurance agreement.
Income Tax Expense. We incur federal income tax expense as well as income tax expense in certain foreign jurisdictions in which we operate.
In the event of a 5% increase in claims frequency as measured by our workers compensation insureds’ payroll, which we believe is the most important assumption regarding our business, our loss reserves as of December 31, 2013 would be understated by $22.8 million and would result in an after tax reduction in shareholders’ equity of $14.8 million. In the event of a 5% increase in claim severity, which is the average incurred loss per claim, our loss and loss adjustment expense reserves would be understated by $12.4 million and would result in an after tax reduction in shareholders’ equity of $8.1 million.
Assessments Related to Insurance Premiums. We are subject to various assessments and premium surcharges related to our insurance activities, including assessments and premium surcharges for state guaranty funds and second injury funds. Assessments based on premiums are generally paid within one year after the calendar year in which the policies are written. Assessments based on losses are generally paid within one year of when claims are paid by us. State insurance regulatory agencies use state guaranty fund assessments to pay claims of policyholders of impaired, insolvent or failed insurance companies and the operating expenses of those agencies. States use second injury funds to reimburse insurers and employers for claims paid to injured employees for aggravation of prior conditions or injuries. In some states, these assessments and premium surcharges may be partially recovered through a reduction in future premium taxes.
Net Realized Gains (Losses) on Investments. We had net realized gains on investments of $15.5 million and $9.0 million for the years ended December 31, 2013 and 2012, respectively. The increase in 2013 resulted from our decision to sell more positions in 2013 than in 2012 as a result of the increase in market values of our equity securities in 2013. We impaired approximately $3 million of investments in 2013 and 2012.
Gross Written Premium. Gross written premium increased $726.2 million, or 77.8%, to $1,660.0 million for the year ended December 31, 2013 from $933.7 million for the year ended December 31, 2012. The increase resulted primarily from the increase in the number of policies issued as well as average policy size. The majority of the increase, which was approximately $506 million, related to workers' compensation policies. The increase came primarily from the states of California, Florida, Illinois, New Jersey, New York and Pennsylvania. The segment also benefited in 2013 from the acquisition of Sequoia and FNIC, which added approximately $110 million of total gross written premium. Additionally, we had an increase in our assigned risk premium of approximately $56 million.
We assumed $118.1 million and $102.6 million of premium from the NGHC Insurers for the years ended December 31, 2012 and 2011, respectively. The increase in assumed premium in 2012 is due to increased premium writing by the NGHC Insurers. Net earned premium increased 13.9% in 2012 compared to 2011 due to the earning cycle of assumed premium written in 2011. Loss and loss adjustment expense increased 12.6% in 2012 compared to 2011 and increased proportionally with net earned premium. The decrease in the net loss ratio in 2012 from 2011 resulted primarily from lower actuarial estimates based on actual losses. The decrease in the net expense ratio in 2012 compared to 2011 resulted from the sliding scale commission structure with NGHC.
As of December 31, 2013, the weighted average duration of our fixed income securities was 5.2 years and had a yield of 3.2%.
Loss and loss expense reserves increased $1,941.8 million and unearned premium increased $907.4 million in 2013 due primarily to higher premium writings in 2013 compared to 2012 as well as assumed amounts from acquisitions in 2013. The increase in reinsurance recoverable is directly related to the increase in loss and loss expense reserves. Debt increased by $258.2 million in 2013 primarily as a result of issuing $250 million of our 6.125% notes due 2023 in August 2013. Accrued expenses and other liabilities increased $244.4 million million primarily from acquisitions and increases in premium taxes, assessments and surcharges payable related to growth in premiums.
We enter into repurchase agreements and reverse repurchase agreements. The agreements are accounted for as collateralized borrowing transactions and are recorded at contract amounts. In the case of repurchase agreements, we receive cash or securities that we invest or hold in short term or fixed income securities. As of December 31, 2013, there were $293.2 million principal amount outstanding at interest rates between 0.12% and 0.47%. We have 9 repurchase agreements with one counter-party totaling $242.3 million and 3 repurchase agreement with a separate counter-party totaling $50.9 million. Interest expense associated with these repurchase agreements for 2013 was $0.8 million of which $0 million was accrued as of December 31, 2013. We have approximately $311.5 million of collateral pledged in support of these agreements. Additionally, during the year ended December 31, 2013, we closed our reverse repurchase agreement and did not incur any gain or loss as a result of this agreement.
We currently own 271 life settlement contracts and 2 premium finance loans with a carrying value of $233.0 million. In order for us to derive the economic benefit of the face value of the policies, we are required to make these premium payments. The contractual obligations are on a consolidated basis. As we have a 50% ownership interest in these life insurance policies and premium finance loans, NGHC has an obligation for 50% of the above contractual obligations.