(6) FINANCIAL INSTRUMENTS

All marketable securities were classified as available-for-sale at June 30, 2018 and December 31, 2017.

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.

The Company’s cash equivalents and marketable securities are classified within Level 2 in the fair value hierarchy because they are valued using third-party pricing sources and remeasured on a recurring basis. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data and other observable inputs. The Company validates the prices provided by its third-party pricing services by understanding the models used, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming those securities traded in active markets. See Note 12 to these Condensed Consolidated Financial Statements for additional information related to the Company’s fair value measurements.

Impairment assessments are made at the individual security level each reporting period. When the fair value of an investment is less than its cost at the balance sheet date, a determination is made as to whether the impairment is other-than-temporary and, if it is other-than-temporary, an impairment loss is recognized in earnings equal to the difference between the investment’s amortized cost and fair value at such date. As of June 30, 2018, the Company’s investments in an unrealized loss position were not significant and were considered to be temporary in nature. The Company has the ability and intent to hold all investments that have been in a continuous loss position until maturity or recovery, thus no other-than-temporary impairment is deemed to have occurred.