5. Investments

Marketable Investments

Held-to-Maturity Investments

Marketable investments classified as held-to-maturity consist of the following (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Government-sponsored enterprises at June 30, 2013	$	342,414	$	187	$	(41	)	$	342,560
Corporate notes and bonds at June 30, 2013	208,311		79		(88		)	208,302
Total	$	550,725	$	266	$	(129	)	$	550,862
Reported under the following captions on the consolidated balance sheet at June 30, 2013:
Current marketable investments	$	353,041
Noncurrent marketable investments	197,684
	$	550,725

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Government-sponsored enterprises at December 31, 2012	$	350,043	$	261	$	(35	)	$	350,269
Corporate notes and bonds at December 31, 2012	280,385		184		(140		)	280,429
Total	$	630,428	$	445	$	(175	)	$	630,698
Reported under the following captions on the consolidated balance sheet at December 31, 2012:
Current marketable investments	$	325,175
Noncurrent marketable investments	305,253
	$	630,428

The following table summarizes gross unrealized losses and the length of time marketable investments have been in a continuous unrealized loss position (in thousands):

	As of June 30, 2013					As of December 31, 2012
	Fair Value		Gross Unrealized Loss			Fair Value		Gross Unrealized Loss
Government-sponsored enterprises:
Continuous unrealized loss position less than one year	$	83,506	$	(41	)	$	72,727	$	(35	)
Continuous unrealized loss position greater than one year	—		—			—		—
	83,506		(41		)	72,727		(35		)
Corporate notes and bonds:
Continuous unrealized loss position less than one year	$	71,358	$	(88	)	$	90,960	$	(140	)
Continuous unrealized loss position greater than one year	—		—			—		—
	71,358		(88		)	90,960		(140		)
Total	$	154,864	$	(129	)	$	163,687	$	(175	)

We attribute the unrealized losses on held-to-maturity securities as of June 30, 2013 and December 31, 2012 to the variability in related market interest rates. We do not intend to sell these securities, nor is it more likely than not that we will be required to sell them prior to the end of their contractual terms. Furthermore, we believe these securities do not expose us to undue market risk or counterparty credit risk. As such, we do not consider these securities to be other than temporarily impaired.

The following table summarizes the contractual maturities of held-to-maturity marketable investments (in thousands):

	June 30, 2013
	Amortized Cost		Fair Value
Due in less than one year	$	353,041	$	353,212
Due in one to two years	197,684		197,650
Due in three to five years	—		—
Due after five years	—		—
Total	$	550,725	$	550,862

Equity Investments

We own less than one percent of the common stock of a public company. Our investment is classified as available-for-sale, reported at fair value based on the quoted market price, and included on the accompanying consolidated balance sheets in noncurrent marketable investments.

Cost Method Investments

As of June 30, 2013, we maintain in the aggregate, non-controlling equity investments of $38.8 million in privately-held corporations. We account for these investments at cost since we do not have the ability to exercise significant influence over these companies and their fair values are not readily determinable. The fair value of these investments has not been estimated at June 30, 2013, as we have not identified any events or developments indicating that their carrying amounts may be impaired. We include these investments within other assets on our accompanying consolidated balance sheets.