The following table summarizes, for available-for-sale fixed maturities in an unrealized loss position at December 31, 2018 and available-for-sale fixed maturities and equity securities in an unrealized loss position at December 31, 2017, respectively, the aggregate fair value and gross unrealized loss categorized by the duration individual securities have been continuously in an unrealized loss position. (1) Effective January 1, 2018, the Company adopted ASU 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See Note A – Summary of Significant Accounting Policies — Recently Adopted Accounting Pronouncements for further discussion. Unrealized losses in the Company's fixed income portfolio are generally the result of interest rate or foreign currency fluctuations. The Company does not intend to sell any fixed income securities in an unrealized loss position at December 31, 2018, and it is not more likely than not that the Company will have to sell any such fixed income security before recovery of its amortized cost basis. Accordingly, the Company does not believe any unrealized losses represent other-than-temporary impairments as of December 31, 2018. The fair value and the cost or amortized cost of fixed income investments at December 31, 2018, organized by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because borrowers have, in some cases, the right to call or prepay obligations with or without call or prepayment penalties. Pre-refunded municipal bonds are classified based on their pre-refunded call dates. Major categories of investment income for the years ended December 31, are summarized as follows: - 50 - 2018 2017 2016 Interest on fixed income securities $ 19,092 $ 15,340 $ 13,254 Dividends on equity securities 4,380 4,611 3,598 Money market funds, Short-term and other 1,529 471 128 25,001 20,422 16,980 Investment expenses (2,953 ) (2,327 ) (2,497 ) Net investment income $ 22,048 $ 18,095 $ 14,483 Fair Value Cost or Amortized Cost One year or less $ 45,858 7.7 % $ 46,150 7.7 % Excess of one year to five years 287,506 48.5 290,743 48.4 Excess of five years to ten years 101,605 17.1 104,571 17.4 Excess of ten years 6,641 1.2 6,410 1.1 Total contractual maturities 441,610 74.5 447,874 74.6 Asset-backed securities 151,035 25.5 152,630 25.4  Total $ 592,645 100.0 % $ 600,504 100.0 2018 2017 Number of Securities Fair Value Gross Unrealized Loss Number of Securities Fair Value Gross Unrealized Loss Fixed income securities: 12 months or less 275 $ 282,646 $ (7,296 ) 459 $ 313,421 $ (2,683 ) Greater than 12 months 217 131,001 (3,497 ) 112 75,638 (2,155 ) Total fixed income securities 492 413,647 (10,793 ) 571 389,059 (4,838 ) Equity securities $^{(1)}$: 12 months or less – – – 65 46,654 (2,218 ) Greater than 12 months – – – – – – Total equity securities – – – 65 46,654 (2,218 ) Total 492 $ 413,647 $ (10,793 ) 636 $ 435,713 $ (7,056 )