Financial Instruments

Cash Equivalents

The Company had $530,806 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 September 30, 2015 and December 31, 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 were classified as follows:



	September 30, 2015		December 31, 2014
Current	$	285,726	$	—
Non-current	4,098		15,414
Total available-for-sale securities	$	289,824	$	15,414

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



	September 30, 2015
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Debt securities
Corporate bonds	$	194,310	$	306	$	(171	)	$	194,445
U.S. government debt	55,073		80		(2		)	55,151
Asset-backed securities	36,081		66		(17		)	36,130
Equity securities	3,804		294		—			4,098
Total available-for-sale securities	$	289,268	$	746	$	(190	)	$	289,824



	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

As of September 30, 2015 and December 31, 2014, net unrealized gains on the Company's available-for-sale securities of $357 and $233, respectively, net of income tax expense of $199 and $131, respectively, were recorded in accumulated other comprehensive income. See Note 13 for the fair value hierarchy of the Company's available-for-sale securities.

As of September 30, 2015, the corporate bond securities held by the Company had maturities ranging between two months to three years, the U.S. government debt securities held by the Company, excluding U.S. government agency mortgage-backed securities, had maturities ranging between four months to three years, the U.S. government agency mortgage-backed securities held by the Company had maturities ranging between five to six years and the asset-backed securities held by the Company had maturities ranging between one to 26 years.

The proceeds from sales and maturities of available-for-sale securities 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 September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Proceeds from sales and maturities of securities	$	1,019	$	—	$	16,056	$	342,045
Gross realized gains	—		—		3,795		1,311
Gross realized losses	—		—		—		(99		)