Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2017

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 March 31, 2017 and December 31, 2016:

	March 31, 2017
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	145,460	$	145,460	$	—	$	—
Total cash equivalents		145,460		145,460		—		—
Marketable securities:
U.S. government securities		91,970		—		91,970		—
U.S. corporate bonds		39,118		—		39,118		—
International corporate bonds		15,181		—		15,181		—
U.S. commercial paper		21,891		—		21,891		—
International commercial paper		28,944		—		28,944		—
Total marketable securities		197,104		—		197,104		—
Total cash equivalents and marketable securities	$	342,564	$	145,460	$	197,104	$	—

	December 31, 2016
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	168,517	$	168,517	$	—	$	—
Total cash equivalents		168,517		168,517		—		—
Marketable securities:
U.S. government securities		100,031		—		100,031		—
U.S. corporate bonds		58,452		—		58,452		—
International corporate bonds		24,190		—		24,190		—
U.S. commercial paper		30,351		—		30,351		—
International commercial paper		15,938		—		15,938		—
Total marketable securities		228,962		—		228,962		—
Total cash equivalents and marketable securities	$	397,479	$	168,517	$	228,962	$	—

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 March 31, 2017 and December 31, 2016:

	March 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities	$	92,026	$	—	$	(56	)	$	91,970
U.S. corporate bonds		39,138		—		(20	)		39,118
International corporate bonds		15,186		—		(5	)		15,181
U.S. commercial paper		21,891		—		—			21,891
International commercial paper		28,944		—		—			28,944
	$	197,185	$	—	$	(81	)	$	197,104

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities	$	100,055	$	2	$	(26	)	$	100,031
U.S. corporate bonds		58,508		—		(56	)		58,452
International corporate bonds		24,212		—		(22	)		24,190
U.S. commercial paper		30,351		—		—			30,351
International commercial paper		15,938		—		—			15,938
	$	229,064	$	2	$	(104	)	$	228,962