The following tables show the Company’s cash, cash equivalents and available-for-sale securities by significant investment category as of June 30, 2018 and December 31, 2017, respectively:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash and Cash Equivalents		Short-term Marketable Securities ⁽¹⁾		Long-term Marketable Securities ⁽²⁾
Level 1:
Cash	$	209,062	$	—	$	—		$	209,062	$	209,062	$	—	$	—

Level 2:
Money market instruments		177,882		—		—			177,882		177,882		—		—
Corporate debt securities		643,979		136		(3,452	)		640,663		7,708		411,185		221,770
Commercial paper		51,818		1		—			51,819		18,947		32,871		—
U.S. government agency securities		532,066		4		(1,597	)		530,473		11,312		461,143		58,019
Foreign and other		33,035		150		(23	)		33,162		2,500		30,463		199
Subtotal		1,438,780		291		(5,072	)		1,433,999		218,349		935,662		279,988

Total	$	1,647,842	$	291	$	(5,072	)	$	1,643,061	$	427,411	$	935,662	$	279,988

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Cash and Cash Equivalents		Short-term Marketable Securities ⁽¹⁾		Long-term Marketable Securities ⁽²⁾
Level 1:
Cash	$	340,253	$	—	$	—		$	340,253	$	340,253	$	—	$	—

Level 2:
Money market instruments		215,441		—		—			215,441		215,441		—		—
Corporate debt securities		707,652		150		(2,553	)		705,249		3,096		406,188		295,965
Commercial paper		24,566		—		—			24,566		2,751		21,815	—
U.S. government agency securities		472,593		—		(1,975	)		470,618		35,497		345,501		89,620
Foreign and other		25,540		150		(64	)		25,626	990			24,436		200
Subtotal		1,445,792		300		(4,592	)		1,441,500		257,775		797,940		385,785

Total	$	1,786,045	$	300	$	(4,592	)	$	1,781,753	$	598,028	$	797,940	$	385,785

(1) The Company’s short-term marketable securities mature in one year or less.

(2) The Company’s long-term marketable securities mature between one and five years.