Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total		Common Stock		Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2018	[1]	$ 234,942		$ 4		$ 357,873	$ (122,828)	$ (107)
Balance, shares at Dec. 31, 2018	[1]			43,610,823
Cumulative effect adjustment upon adoption of ASC 606 | ASC 606		2,212					2,212
Issuance of common stock upon exercise of stock options, shares				69
Vesting of early exercised stock options and restricted stock		273				273
Vesting of early exercised stock options and restricted stock, shares				114,934
Stock-based compensation		1,674				1,674
Other comprehensive income (loss)		136						136
Net loss		(17,670)					(17,670)
Balance at Mar. 31, 2019		221,567		$ 4		359,820	(138,286)	29
Balance, shares at Mar. 31, 2019				43,725,826
Balance at Dec. 31, 2018	[1]	234,942		$ 4		357,873	(122,828)	(107)
Balance, shares at Dec. 31, 2018	[1]			43,610,823
Net loss		(45,760)
Balance at Jun. 30, 2019		196,646		$ 4		362,905	(166,376)	113
Balance, shares at Jun. 30, 2019				43,934,108
Balance at Mar. 31, 2019		221,567		$ 4		359,820	(138,286)	29
Balance, shares at Mar. 31, 2019				43,725,826
Issuance of common stock upon exercise of stock options		99				99
Issuance of common stock upon exercise of stock options, shares				17,649
Vesting of early exercised stock options and restricted stock		260				260
Vesting of early exercised stock options and restricted stock, shares				107,952
Issuance of common stock under Employee Stock Purchase Plan		596				596
Issuance of common stock under Employee Stock Purchase Plan, shares				82,681
Stock-based compensation		2,130				2,130
Other comprehensive income (loss)		84						84
Net loss		(28,090)					(28,090)
Balance at Jun. 30, 2019		196,646		$ 4		362,905	(166,376)	113
Balance, shares at Jun. 30, 2019				43,934,108
Balance at Dec. 31, 2019	[1]	$ 163,842	[2]	$ 4		369,100	(205,326)	64
Balance, shares at Dec. 31, 2019		45,925,004		44,212,195	[1]
Issuance of common stock upon exercise of stock options		$ 643				643
Issuance of common stock upon exercise of stock options, shares				59,939
Vesting of early exercised stock options and restricted stock		220				220
Vesting of early exercised stock options and restricted stock, shares				77,388
Stock-based compensation		3,462				3,462
Other comprehensive income (loss)		224						224
Net loss		(27,753)					(27,753)
Balance at Mar. 31, 2020		140,638		$ 4		373,425	(233,079)	288
Balance, shares at Mar. 31, 2020				44,349,522
Balance at Dec. 31, 2019	[1]	$ 163,842	[2]	$ 4		369,100	(205,326)	64
Balance, shares at Dec. 31, 2019		45,925,004		44,212,195	[1]
Net loss		$ (72,827)
Balance at Jun. 30, 2020		$ 428,710		$ 6		706,713	(278,153)	144
Balance, shares at Jun. 30, 2020		58,940,933		57,372,168
Balance at Mar. 31, 2020		$ 140,638		$ 4		373,425	(233,079)	288
Balance, shares at Mar. 31, 2020				44,349,522
Issuance of common stock in public offering, net of $21,629 offering costs		326,246		$ 2		326,244
Issuance of common stock in public offering, net of $21,629 offering costs, shares				12,650,000
Issuance of common stock upon exercise of stock options		1,751				1,751
Issuance of common stock upon exercise of stock options, shares				216,286
Vesting of early exercised stock options and restricted stock		216				216
Vesting of early exercised stock options and restricted stock, shares				64,501
Issuance of common stock under Employee Stock Purchase Plan		607				607
Issuance of common stock under Employee Stock Purchase Plan, shares				91,859
Stock-based compensation		4,470				4,470
Other comprehensive income (loss)		(144)						(144)
Net loss		(45,074)					(45,074)
Balance at Jun. 30, 2020		$ 428,710		$ 6		$ 706,713	$ (278,153)	$ 144
Balance, shares at Jun. 30, 2020		58,940,933		57,372,168

[1] The balances as of December 31, 2019 and 2018 have been derived from the audited financial statements as of that date.

[2] The Condensed Consolidated Balance Sheet as of December 31, 2019 has been derived from the audited financial statements as of that date.