Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value of Financial Instruments

Summary of valuation of the financial instruments

	Fair Value Measurements at June 30, 2018 Using
Description	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents:
Money market funds	$	82,111	$	—	$	—	$	82,111
Corporate debt securities	—		23,906		—		23,906
Government debt securities	—		8,359		—		8,359
Total cash equivalents	$	82,111	$	32,265	$	—	$	114,376
Short-term investments:
Government debt securities	$	71,459	$	124,322	$	—	$	195,781
Corporate debt securities	—		151,635		—		151,635
Total short-term investments	$	71,459	$	275,957	$	—	$	347,416
Other assets, net:
Auction rate securities	$	—	$	—	$	5,642	$	5,642
Total	$	—	$	—	$	5,642	$	5,642
Total	$	153,570	$	308,222	$	5,642	$	467,434

	Fair Value Measurements at December 30, 2017 Using
Description	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other  Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents:
Money market funds	$	106,047	$	—	$	—	$	106,047
Corporate debt securities	—		11,231		—		11,231
Government debt securities	53,615		1,453		—		55,068
Total cash equivalents	$	159,662	$	12,684	$	—	$	172,346
Short-term investments:
Government debt securities	$	94,575	$	228,247	$	—	$	322,822
Corporate debt securities	—		171,835		—		171,835
Total short-term investments	$	94,575	$	400,082	$	—	$	494,657
Other assets, net:
Auction rate securities	$	—	$	—	$	5,681	$	5,681
Total	$	—	$	—	$	5,681	$	5,681
Total	$	254,237	$	412,766	$	5,681	$	672,684

Summarization of contractual underlying maturities of available-for-sale investments

The following summarizes the contractual underlying maturities of the Company’s available-for-sale investments at June 30, 2018 (in thousands):

	Cost		Fair Value
Due in one year or less	$	313,832	$	313,333
Due after one year through ten years	131,655		130,420
Due after ten years	24,042		23,681
	$	469,529	$	467,434

Schedule of available-for-sale investments in continuous unrealized loss position by length of time

The available-for-sale investments that were in a continuous unrealized loss position, aggregated by length of time that individual securities have been in a continuous loss position, were as follows (in thousands):

	Less Than 12 Months					12 Months or Greater					Total
As of June 30, 2018	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Government debt securities	$	153,566	$	(893	)	$	3,269	$	(6	)	$	156,835	$	(899	)
Corporate debt securities	126,879		(790		)	11,152		(70		)	138,031		(860		)
Auction rate securities	—		—			5,642		(358		)	5,642		(358		)
	$	280,445	$	(1,683	)	$	20,063	$	(434	)	$	300,508	$	(2,117	)

	Less Than 12 Months					12 Months or Greater					Total
As of December 30, 2017	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Government debt securities	$	244,880	$	(931	)	$	3,027	$	(15	)	$	247,907	$	(946	)
Corporate debt securities	151,149		(447		)	11,578		(73		)	162,727		(520		)
Auction rate securities	—		—			5,681		(319		)	5,681		(319		)
	$	396,029	$	(1,378	)	$	20,286	$	(407	)	$	416,315	$	(1,785	)

Summary of quantitative information about level 3 fair value measurements

Auction rate securities

Fair Value at June 30, 2018 (000s)		Valuation Technique	Unobservable Input	Weighted Average
$	5,642	Discounted cash flow	Estimated yield	2.56%
			Expected holding period	10 years
			Estimated discount rate	3.82%

Summary of activity in Level 3 financial instruments

The following summarizes the activity in Level 3 financial instruments for the three and six months ended June 30, 2018 (in thousands):

Assets

Auction Rate Securities	Three Months Ended		Six Months Ended
Beginning balance	$	5,609	$	5,681
Gain (loss) included in other comprehensive loss	33		(39		)
Balance at June 30, 2018	$	5,642	$	5,642