Financial Instruments

Cash Equivalents

The Company had $376,901 and $221,918 of held-to-maturity securities with original maturities of three months or less, primarily consisting of corporate debt securities, classified as cash equivalents at June 30, 2016 and December 31, 2015, respectively. The Company's investments in held-to-maturity securities are held at amortized cost, which approximates fair value.

Available-for-Sale Marketable Securities

Investments in available-for-sale securities were classified as follows:



	June 30, 2016		December 31, 2015
Current	$	352,021	$	520,144
Non-current	109,337		48,081
Total available-for-sale securities	$	461,358	$	568,225

The cost, gross unrealized gains, gross unrealized losses and fair value of the Company's available-for-sale securities were as follows:



	June 30, 2016
	Cost		Gross Unrealized Gains		Gross Unrealized Losses ⁽¹⁾			Fair Value
Debt securities
Corporate bonds	$	219,971	$	1,162	$	(16	)	$	221,117
U.S. government debt ⁽²⁾	72,702		462		—			73,164
Asset-backed securities	57,546		197		(3		)	57,740
Equity securities	60,281		49,194		(138		)	109,337
Total available-for-sale securities	$	410,500	$	51,015	$	(157	)	$	461,358



	December 31, 2015
	Cost		Gross Unrealized Gains		Gross Unrealized Losses ⁽¹⁾			Fair Value
Debt securities
Corporate bonds	$	336,665	$	55	$	(1,076	)	$	335,644
U.S. government debt ⁽²⁾	135,226		2		(374		)	134,854
Asset-backed securities	49,759		2		(115		)	49,646
Equity securities	54,371		466		(6,756		)	48,081
Total available-for-sale securities	$	576,021	$	525	$	(8,321	)	$	568,225

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(1)	All unrealized loss positions were held at a loss for less than 12 months.


(2)	U.S. Treasury obligations, U.S. government agency obligations and U.S government agency mortgage-backed securities.

As of June 30, 2016 and December 31, 2015, net unrealized gains (losses) on the Company's available-for-sale securities of $32,585 and $(4,995), respectively, net of income tax expense (benefit) of $18,273 and $(2,801), respectively, were recorded in accumulated other comprehensive loss. See Note 13 for the fair value hierarchy of the Company's available-for-sale securities.

As of June 30, 2016, the corporate bond securities held by the Company had maturities ranging between one month to five years; the U.S. government debt securities held by the Company, excluding U.S. government agency mortgage-backed securities, had maturities ranging between one to three years; the U.S. government agency mortgage-backed securities held by the Company had maturities of approximately five years; and the asset-backed securities held by the Company had maturities ranging between one to five years.

The proceeds from sales and maturities of available-for-sale securities included in the consolidated statements of cash flows and the gross realized gains and losses included in the consolidated statements of operations are reflected in the table below. The cost of securities sold was determined using the specific identification method.



	Three Months Ended June 30,					Six Months Ended June 30,
	2016			2015		2016			2015
Proceeds from sales and maturities of securities	$	275,573		$	15,037	$	302,432		$	15,037
Gross realized gains	1,280			3,795		1,341			3,795
Gross realized losses	(13		)	—		(22		)	—