(7) INVESTMENTS

All investments were classified as available-for-sale at March 31, 2016 and December 31, 2015. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s available-for-sale securities by major security type at March 31, 2016 and December 31, 2015 are summarized in the tables below:

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value at March 31, 2016
Certificates of deposit	$	11,517	$	—	$	—		$	11,517
Corporate debt securities		321,358		1,161		(164	)		322,355
Commercial paper		6,247		—		—			6,247
U.S. government agency securities		160,376		210		(25	)		160,561
Greek government-issued bonds		47		77		—			124
Total	$	499,545	$	1,448	$	(189	)	$	500,804

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value at December 31, 2015
Certificates of deposit	$	63,919	$	1	$	—		$	63,920
Corporate debt securities		358,625		20		(732	)		357,913
Commercial paper		12,733		—		—			12,733
U.S. government agency securities		186,882		—		(344	)		186,538
Greek government-issued bonds		48		79		—			127
Total	$	622,207	$	100	$	(1,076	)	$	621,231

The Company has two investments in marketable equity securities measured using quoted prices in their respective active markets that are collectively considered strategic investments. As of March 31, 2016, the fair value of the Company’s marketable equity securities was $8.1 million, which included an unrealized gain of $2.8 million. As of December 31, 2015, the fair value of the Company’s marketable equity securities was $18.1 million, which included an unrealized gain of $12.7 million. These investments are recorded in Other Assets in the Company’s Condensed Consolidated Balance Sheets.

The fair values of available-for-sale securities by contractual maturity were as follows:

	March 31,		December 31,
	2016		2015
Maturing in one year or less	$	186,400	$	195,579
Maturing after one year through five years		314,404		425,652
Total	$	500,804	$	621,231

Impairment assessments are made at the individual security level each reporting period. When the fair value of an investment is less than its cost at the balance sheet date, a determination is made as to whether the impairment is other-than-temporary and, if it is other-than-temporary, an impairment loss is recognized in earnings equal to the difference between the investment’s amortized cost and fair value at such date. As of March 31, 2016, some of the Company’s investments were in an unrealized loss position. However, the Company has the ability and intent to hold all investments that have been in a continuous loss position until maturity or recovery, thus no other-than-temporary impairment is deemed to have occurred.

See Note 13 to these Condensed Consolidated Financial Statements for additional discussion regarding the fair value of the Company’s available-for-sale securities.