4. Investments

The Company’s trading securities consist of the following:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value (Net Carrying Amount)
December 31, 2015
Trading equity securities	$	4,160	$	79	$	188	$	4,05
Trading debt securities		9,263		37		272		9,028
Total	$	13,423	$	116	$	460	$	13,079
December 31, 2014
Trading equity securities	$	4,335	$	374		9	$	4,700
Trading debt securities		8,573		107		71		8,609
Total	$	12,908	$	481	$	80	$	13,309

Trading equity investments are valued at their estimated fair value based on their quoted market prices and trading debt securities are valued based upon a mix of observable market prices and model driven prices derived from a matrix of observable market prices for assets with similar characteristics obtained from a nationally recognized third party pricing service. Additionally, a significant portion of the trading equity securities are in equity money market and mutual funds and also comprise a portion of the Company’s liability under its SERP. See Note 12, Pension and Retirement Plans, for additional information on these investments and the SERP.

Trading debt securities are comprised mainly of marketable debt securities held by Astec Insurance. Astec Insurance has an investment strategy that focuses on providing regular and predictable interest income from a diversified portfolio of high-quality fixed income securities.

Net unrealized gains or losses incurred on investments still held as of the end of each reporting period amounted to losses of $429 and $17 in 2015 and 2014, respectively and a gain of $175 in 2013.