Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of Fair Value by Significant Investment Category

The following table summarizes the Company’s cash and available-for-sale securities’ amortized cost, unrealized gains (losses), and fair value by significant investment category reported as cash and cash equivalents, restricted cash, marketable securities, or long-term investments as of September 30, 2019 and December 31, 2018.

(in thousands)									Reported as:
September 30, 2019	Amortized Cost		Unrealized Gain		Unrealized (Loss)		Fair Value		Cash & Cash Equivalents		Marketable Securities		Long-term Investments		Long- term Restricted Cash
Cash	$	2,202	$	—	$	—	$	2,202	$	2,202	$	—	$	—	$	—
Level I:
Money market funds	506,164		—		—		506,164		499,504		—		—		6,660
Level II:
Corporate bonds	15,030		23		—		15,053		—		8,988		6,066		—
U.S. treasury securities	115,550		80		—		115,630		—		105,526		10,103		—
U.S. government agency securities	1,100		—		—		1,100		—		1,100		—		—
Commercial paper	27,785		—		—		27,785		—		27,785		—		—
Subtotal	159,465		103		—		159,568		—		143,399		16,169		—
Total assets measured at fair value on a recurring basis	$	667,831	$	103	$	—	$	667,934	$	501,706	$	143,399	$	16,169	$	6,660

(in thousands)									Reported as:
December 31, 2018	Amortized Cost		Unrealized Gain		Unrealized (Loss)		Fair Value		Cash & Cash Equivalents		Marketable Securities		Long-term Investments		Long-term Restricted Cash
Cash	$	4,151	$	—	$	—	$	4,151	$	4,151	$	—	$	—	$	—
Level I:
Money market funds	23,278		—		—		23,278		16,907		—		—		6,371
Level II:
Corporate bonds	17,291		1		(16)		17,276		—		17,276		—		—
U.S. treasury securities	102,360		8		(20)		102,348		—		102,348		—		—
U.S. government agency securities	1,099		—		—		1,099		—		1,099		—		—
Commercial paper	18,876		—		—		18,876		3,997		14,879		—		—
Subtotal	139,626		9		(36)		139,599		3,997		135,602		—		—
Total assets measured at fair value on a recurring basis	$	167,055	$	9	$	(36)	$	167,028	$	25,055	$	135,602	$	—	$	6,371

Schedule of Redeemable Convertible Preferred Stock Warrant Liability Measured and Recorded at Fair Value

The following tables summarize the Company’s redeemable convertible preferred stock warrant liability measured and recorded at fair value as of September 30, 2019 and December 31, 2018:

	September 30, 2019
	Fair Value		Reported as Long-Term Liability
	(in thousands)
Fair value using Level III inputs
Redeemable convertible preferred stock warrant liability	$	3,135	$	3,135
Reclassification to stockholders' equity (deficit)	(3,135)		(3,135)
Balance as of September 30, 2019	$	—	$	—

	December 31, 2018
	Fair Value		Reported as Long-Term Liability
	(in thousands)
Fair value using Level III inputs
Redeemable convertible preferred stock warrant liability	$	1,618	$	1,618
Balance as of December 31, 2018	$	1,618	$	1,618

	Redeemable Convertible Preferred Stock Warrant Liability
	(in thousands)
Balance as of December 31, 2018	$	1,618
Addition	—
Change in fair value	1,517
Conversion of redeemable convertible preferred stock warrants into Class B common stock warrants	(3,135)
Balance as of September 30, 2019	$	—