Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Cash and Cash Equivalents, Available-for-sale Securities Reconciliation

The Company's cash and cash equivalents, short-term investments, and long-term investments consist of the following:

	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Cash and cash equivalents:
Cash	$	40,913	$	—	$	—		$	40,913
Money market funds	113		—		—			113
Total	41,026		—		—			41,026
Short-term marketable securities:
Commercial paper	3,237		—		—			3,237
Corporate bonds	30,906		—		(84		)	30,822
Asset-backed securities	10,447		—		(15		)	10,432
U.S. government agencies	203,734		9		(94		)	203,649
Total	248,324		9		(193		)	248,140
Long-term marketable securities:
Asset-backed securities	22,945		10		(28		)	22,927
U.S. government agencies	18,804		—		(53		)	18,751
Corporate bonds	35,322		3		(293		)	35,032
Total	77,071		13		(374		)	76,710
Total	$	366,421	$	22	$	(567	)	$	365,876

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Cash and cash equivalents:
Cash	$	86,500	$	—	$	—		$	86,500
Money market funds	91		—		—			91
Total	86,591		—		—			86,591
Short-term investments:
Commercial paper	12,623		—		(3		)	12,620
Corporate bonds	38,425		1		(64		)	38,362
U.S. government agencies	151,058		—		(217		)	150,841
Total	202,106		1		(284		)	201,823
Long-term investments:
Asset-backed securities	4,998		—		(12		)	4,986
U.S. government agencies	24,269		—		(54		)	24,215
Corporate bonds	38,198		—		(175		)	38,023
Total	67,465		—		(241		)	67,224
Total	$	356,162	$	1	$	(525	)	$	355,638

Schedule of Assets Measured on Recurring Basis

The following table sets forth by level within the fair value hierarchy the fair value of the Company's available-for-sale securities measured on a recurring basis, excluding cash and money market funds:

	December 31, 2018
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Commercial paper	$	—	$	3,237	$	—	$	3,237
U.S. government agencies	—		222,400		—		222,400
Corporate bonds	—		65,854		—		65,854
Asset-backed securities	—		33,359		—		33,359
Total	$	—	$	324,850	$	—	$	324,850

	December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Commercial paper	$	—	$	12,620	$	—	$	12,620
U.S. government agencies	—		175,056		—		175,056
Corporate bonds	—		76,385		—		76,385
Asset-backed securities	—		4,986		—		4,986
Total	$	—	$	269,047	$	—	$	269,047

Schedule of Investments Classified by Contractual Maturity

The following summarizes the fair value of securities classified as available-for-sale by contractual maturity:

	December 31, 2018
	Mature within One Year		After One Year through Two Years		Over Two Years		Fair Value
	(in thousands)
Commercial paper	$	3,237	$	—	$	—	$	3,237
U.S. government agencies	203,649		18,751		—		222,400
Corporate bonds	30,822		33,531		1,501		65,854
Asset-backed securities	29,026		4,333		—		33,359
Total	$	266,734	$	56,615	$	1,501	$	324,850