Cash Equivalents

The Company had $221,918 and $509,811 of held-to-maturity securities with original maturities of three months or less, primarily consisting of corporate debt securities, classified as cash equivalents at December 31, 2015 and 2014, 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 at December 31 were classified as follows:



	2015		2014
Current	$	520,144	$	—
Non-current	48,081		15,414
Total available-for-sale securities	$	568,225	$	15,414

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



	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



	December 31, 2014
	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Equity securities	$	15,050	$	364	$	—	$	15,414
Total available-for-sale securities	$	15,050	$	364	$	—	$	15,414

______________________________


(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 December 31, 2015 and December 31, 2014, net unrealized (losses) gains on the Company's available-for-sale securities of $(4,995) and $233, respectively, net of income tax (benefit) expense of $(2,801) and $131, respectively, were recorded in accumulated other comprehensive income. See Note 14 for the fair value hierarchy of the Company's available-for-sale securities.

As of December 31, 2015, the corporate bond securities held by the Company had maturities ranging between three months 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 month 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 six 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.



	Year Ended December 31,
	2015			2014			2013
Proceeds from sales and maturities of securities	$	48,900		$	342,045		$	7,770
Gross realized gains	3,830			1,311			20
Gross realized losses	(32		)	(99		)	(39		)