Deferred acquisition costs increased 52.1% to $335.8 million at December 31, 2015, primarily due to a $105.8 million decrease in the impact of the change in net unrealized appreciation on fixed maturity securities during the period. Securities and indebtedness of related parties increased 3.6% to $134.6 million primarily due to additional investments made in equity investees specializing in low income housing and other income partnerships. Assets held in separate accounts decreased 8.5% to $625.3 million primarily due to market performance on the underlying investment portfolios. Cash and cash equivalents decreased 61.5% to $29.5 million primarily due to normal fluctuations in timing of payments made and received.
Pension assets and liabilities are affected by the estimated fair value of plan assets, estimates of the expected return on plan assets and/or discount rates. Actual changes in the fair value of plan assets and differences between the actual return on plan assets and the expected return on plan assets will affect the amount of pension expense ultimately recognized. The December 31, 2015 pension obligation was computed based on an average 4.65% discount rate, which was based on yields for high-quality corporate bonds with a maturity approximating the duration of our pension liability. The long-term return on plan assets is based on current and projected asset allocations. Declines in comparable bond and equity yields would increase our net pension liability. Our net pension liability could increase or decrease depending on the extent to which returns on pension plan assets are lower or higher than the discount rate.
At December 31, 2015, our fixed maturity securities classified as available for sale had a fair value of $6,637.8 million, with gross unrealized gains totaling $412.9 million and gross unrealized losses totaling $155.1 million. Due to the large number of fixed maturity securities held, the unique attributes of each security and the complexity of valuation methods, it is not practical to estimate a potential range of fair values for different assumptions and methods that could be used in the valuation process.
The long-term rate of return may fluctuate over time based on asset mix and if investment returns over a long period of time significantly differ from historical returns. The discount rate changes annually as it is based on current yields for high-quality corporate bonds with a maturity approximating the duration of our pension obligations. As fluctuations in the expected long-term rate of return and discount rate have been historically moderate and we have no current plans to change our investment strategy significantly, we believe a change of up to 100 basis points is reasonably likely. A 100 basis point decrease in the expected return on assets would result in a $0.8 million increase in pension expense and a 100 basis point increase would result in a $0.8 million decrease to pension expense. A 100 basis point decrease in the assumed discount rate would result in a $2.1 million increase in pension expense while a 100 basis point increase would result in a $1.9 million decrease to pension expense. The information above is for illustrative purposes only and does not reflect our expectations regarding future changes in the long-term rate of return or discount rates.
Real estate is reported at cost less allowances for depreciation, as applicable. The carrying value of these assets is subject to regular review. For properties held for investment, if indicators of impairment are present and a property's expected undiscounted cash flows are not sufficient to recover the property's carrying value, an impairment loss is recognized and the property's cost basis is reduced to fair value. Real estate held for sale is carried at the lower of cost or fair value, less costs to sell, with valuation allowances recognized as a realized loss on investments and depreciation is no longer recorded. There was one property held for investment with an impairment charge of $0.2 million as of December 31, 2015 and two properties held for investment with an impairment charge of $0.4 million as of December 31, 2014. There were no properties held for sale as of December 31, 2015 or December 31, 2014.
Excluding mortgage- and asset-backed securities, no securities from the same issuer had an aggregate unrealized loss in excess of $4.7 million at December 31, 2015, with the largest unrealized loss from an energy service provider. With respect to mortgage- and asset-backed securities not backed by the United States Government, our largest aggregate unrealized loss from the same issuer at December 31, 2015 was $3.7 million, consisting of two different securities that are backed by different pools of Alt-A residential mortgage loans. Both securities are rated non-investment grade and the largest unrealized loss totaled $2.2 million.
The carrying value of investments which have been non-income producing for the twelve months preceding December 31, 2015 includes real estate totaling $2.0 million.
The tables above exclude certain securities for which the fair value was based on non-binding broker quotes where we could not reasonably obtain the quantitative unobservable inputs.
We continue to invest in LIHTC which generate pre-tax losses but after-tax gains as the related tax credits are realized. The timing of the realization of tax credits is subject to fluctuation from period to period due to the timing of housing project completions and the approval of tax credits. These tax credits, which are reported in equity income, totaled $13.5 million in 2015, $12.2 million in 2014 and $9.8 million in 2013.
In March 2015, the Board of Directors approved a special $2.00 per share cash dividend payable to Class A and Class B common shareholders totaling $49.5 million. In August 2013, we declared a special $2.00 per share cash dividend payable to Class A and Class B common shareholders totaling $51.4 million.
The other defined benefit plans (the Other Plans) provide benefits in addition to those offered under the Multiemployer Plan to certain of our employees or those of our affiliates. These non-qualified benefit plans are not funded, with contributions provided as current benefit obligations become due. Net periodic pension cost of the Other Plans is allocated between the subsidiaries of FBL Financial Group, Inc. and the Farm Bureau affiliated property-casualty companies on a basis of time incurred by the respective employees for each company.
The amount payable per unit awarded is equal to the price per share of the Company's common stock at settlement of the award, and as such, we measure the value of the award each reporting period based on the current stock price. The effects of changes in the stock price during the service period are recognized as compensation cost over the service period.