Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at (in shares) at Dec. 31, 2016		21,529,000
Balances at at Dec. 31, 2016		$ 2	$ 281,900	$ (57)	$ (269,540)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)		3,450,000
Issuance of common stock net of issuance costs	$ 56,486	$ 0	56,486
Issuance of common stock for employee stock purchase plan (in shares)		139,000
Issuance of common stock for employee stock purchase plan	1,793		1,793
Issuance of common stock warrants	674		674
Exercise of stock options (in shares)		228,000
Exercise of stock options	1,086		1,086
Exercise of common stock warrant, net (in shares)		29,000
Exercise of common stock warrants, net	0		0
Vesting of restricted stock units (in shares)		46,000
Stock-based compensation	11,369		11,369
Net loss	(43,562)				(43,562)
Other comprehensive loss	(42)			(42)
Balance at (in shares) at Dec. 31, 2017		25,421,000
Balances at at Dec. 31, 2017	40,109	$ 2	353,308	(99)	(313,102)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)		4,600,000
Issuance of common stock net of issuance costs	53,829	$ 1	53,828
Issuance of common stock for employee stock purchase plan (in shares)		257,000
Issuance of common stock for employee stock purchase plan	1,451		1,451
Issuance of common stock warrants	4,593		4,593
Exercise of stock options (in shares)		431,000
Exercise of stock options	3,507		3,507
Exercise of common stock warrant, net (in shares)		118,000
Exercise of common stock warrants, net	0		0
Vesting of restricted stock units (in shares)		86,000
Stock-based compensation	11,475		11,475
Net loss	(77,400)				(77,400)
Other comprehensive loss	59			59
Balance at (in shares) at Dec. 31, 2018		30,913,000
Balances at at Dec. 31, 2018	36,869	$ 3	428,162	(40)	(391,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)		3,175,000
Issuance of common stock net of issuance costs	68,273	$ 1	68,273
Issuance of common stock for employee stock purchase plan (in shares)		203,000
Issuance of common stock for employee stock purchase plan	1,952		1,952
Issuance of common stock warrants	$ 3,197		3,196
Exercise of stock options (in shares)	1,416,185	2,007,000
Exercise of stock options	$ 18,387		18,387
Tax payments from shares withheld for equity awards	(1,474)		(1,474)
Stock-based compensation	17,458		17,458
Net loss	(40,696)				(40,696)
Other comprehensive loss	185			185
Balance at (in shares) at Dec. 31, 2019		36,298,000
Balances at at Dec. 31, 2019	$ 104,151	$ 4	$ 535,954	$ 145	$ (431,952)