3. Investments

As of December 31, 2017 and 2016, our investments consisted of U.S. treasury notes with maturities up to approximately one year and were classified as available-for-sale. Fair value of U.S. treasury notes is measured on a recurring basis based on Level 1 inputs (quoted prices for identical assets in active markets).

The following is a summary of available-for-sale securities:



	December 31,		December 31,
	2017		2016
Amortized cost	$	324,875	$	455,109
Unrealized gains (losses)		(493)		(218)
Fair value	$	324,382	$	454,891

The following is a summary of unrealized gains (losses) on available-for-sale securities recorded in other comprehensive income (loss) in the consolidated statement of comprehensive income:



	Year ended December 31,
	2017		2016		2015
Unrealized gains (losses) on available-for-sale securities	$	(274)	$	2,251	$	(2,468)
Unrealized gains (losses) on available-for-sale securities, net of tax	$	(186)	$	1,402	$	(1,522)

Realized gains and losses on available-for-sale securities are recorded in interest and other income on the consolidated statement of income. We had no realized gains or losses for the years ended December 31, 2017 and 2015, and $547 of realized gains on available-for-sale securities for the year ended December 31, 2016. During the year ended December 31, 2015, we recorded an other-than-temporary impairment charge of $244 in interest and other income in the consolidated statement of income in connection with a decline in the fair market value of certain available-for-sale securities.

We have elected to fund certain deferred compensation obligations through a rabbi trust, the assets of which are designated as trading securities, as described further in Note 7. “Employee Benefit Plans.”