Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Company's Money Market Funds and Marketable Securities

The following tables summarize the Company’s money market funds and marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Cash equivalents	$	126,705	$	65,414	$	61,291	$	—
Total cash equivalents		126,705		65,414		61,291		—
Marketable securities:
U.S. government securities		205,328		—		205,328		—
U.S. corporate bonds		429,845		—		429,845		—
International corporate bonds		142,998		—		142,998		—
U.S. commercial paper		52,261		—		52,261		—
International commercial paper		51,256		—		51,256		—
Total marketable securities		881,688		—		881,688		—
	$	1,008,393	$	65,414	$	942,979	$	—

	December 31, 2018
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Cash equivalents	$	190,943	$	190,943	$	—	$	—
Total cash equivalents		190,943		190,943		—		—
Marketable securities:
U.S. government securities		220,482		—		220,482		—
U.S. corporate bonds		258,566		—		258,566		—
International corporate bonds		78,468		—		78,468		—
U.S. commercial paper		77,611		—		77,611		—
International commercial paper		96,706		—		96,706		—
Total marketable securities		731,833		—		731,833		—
	$	922,776	$	190,943	$	731,833	$	—

Summary of Gross Unrealized Gains and Losses of Marketable Securities

The following tables summarize the gross unrealized gains and losses of the Company’s marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities	$	205,172	$	176	$	(20	)	$	205,328
U.S. corporate bonds		429,148		797		(100	)		429,845
International corporate bonds		142,568		457		(27	)		142,998
U.S. commercial paper		52,252		14		(5	)		52,261
International commercial paper		51,253		5		(2	)		51,256
	$	880,393	$	1,449	$	(154	)	$	881,688

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities	$	220,531	$	8	$	(57	)	$	220,482
U.S. corporate bonds		258,876		6		(316	)		258,566
International corporate bonds		78,600		—		(132	)		78,468
U.S. commercial paper		77,630		8		(27	)		77,611
International commercial paper		96,711		8		(13	)		96,706
	$	732,348	$	30	$	(545	)	$	731,833