CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		42,148,247
Beginning balance at Dec. 31, 2018	$ 194,525	$ 42	$ 386,830	$ (153)	$ (192,194)
Total Stockholders’ Equity
Issuance of warrant in connection with Term Loan	284		284
Issuance of common stock under equity incentive plans (in shares)		527,859
Issuance of common stock under equity incentive plans	737	$ 1	736
Stock-based compensation	2,658		2,658
Net unrealized gain (loss) on available-for-sale investments, net of tax	302			302
Net loss	(37,897)				(37,897)
Ending balance (in shares) at Mar. 31, 2019		42,676,106
Ending balance at Mar. 31, 2019	$ 160,609	$ 43	390,508	149	(230,091)
Beginning balance (in shares) at Dec. 31, 2019	49,913,232	49,763,176
Beginning balance at Dec. 31, 2019	$ 263,883	$ 50	632,647	193	(369,007)
Total Stockholders’ Equity
Issuance of common stock under equity incentive plans (in shares)		150,056
Issuance of common stock under equity incentive plans	550	$ 0	550
Stock-based compensation	8,374		8,374
Net unrealized gain (loss) on available-for-sale investments, net of tax	(232)			(232)
Net loss	$ (74,114)				(74,114)
Ending balance (in shares) at Mar. 31, 2020	49,913,232	49,913,232
Ending balance at Mar. 31, 2020	$ 198,461	$ 50	$ 641,571	$ (39)	$ (443,121)