Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of financial assets measured at fair value on a recurring basis

The following tables provide the financial assets measured at fair value on a recurring basis:

	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months			Gross Unrealized Losses More Than 12 Months		Fair Value Hierarchy as of December 31, 2019						Aggregate Fair Value
										Level 1		Level 2		Level 3
Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	153,252	$	—	$	—		$	—	$	153,252	$	—	$	—	$	153,252
Reverse repurchase agreements	35,800		—		—			—		—		35,800		—		35,800
Total included in cash and cash equivalents	189,052		—		—			—		153,252		35,800		—		189,052
Marketable securities:
U.S. Treasury securities	215,847		241		(3		)	—		216,085		—		—		216,085
Corporate debt securities and commercial paper	1,378,487		4,516		(55		)	—		5,000		1,377,948		—		1,382,948
Total marketable securities	1,594,334		4,757		(58		)	—		221,085		1,377,948		—		1,599,033
Strategic investments	5,500		—		—			—		—		—		5,500		5,500
Total financial assets	$	1,788,886	$	4,757	$	(58	)	$	—	$	374,337	$	1,413,748	$	5,500	$	1,793,585

	Amortized Cost or Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses Less Than 12 Months				Gross Unrealized Losses More Than 12 Months			Fair Value Hierarchy as of December 31, 2018						Aggregate Fair Value
												Level 1		Level 2		Level  3
Financial Assets:	(In thousands)
Cash and cash equivalents:
Money market funds	$	420,234	$	—	$	—			$	—		$	420,234	$	—	$	—	$	420,234
Reverse repurchase agreements	35,000		—		—				—			—		35,000		—		35,000
Commercial paper	9,983		—		—				—			—		9,983		—		9,983
Total included in cash and cash equivalents	465,217		—		—			—	—			420,234		44,983		—		465,217
Marketable securities:
U.S. Treasury securities	59,785		—		(7		)		(9		)	59,769		—		—		59,769
Corporate debt securities and commercial paper	201,683		23		(123		)		(224		)	—		201,359		—		201,359
Total marketable securities	261,468		23		(130		)		(233		)	59,769		201,359		—		261,128
Total financial assets	$	726,685	$	23	$	(130	)		$	(233	)	$	480,003	$	246,342	$	—	$	726,345

Schedule of contractual maturities of marketable securities

The following table summarizes the contractual maturities of marketable securities:

	As of December 31, 2019				As of December 31, 2018
	Amortized Cost		Aggregate Fair Value		Amortized Cost		Aggregate Fair Value
Financial Assets:	(In thousands)
Less than one year	$	859,996	$	861,181	$	261,468	$	261,128
One to three years	734,338		737,852		—		—
Total	$	1,594,334	$	1,599,033	$	261,468	$	261,128