Stockholders' equity - Additional Information (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jan. 01, 2022 shares	Jul. 07, 2020 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) offering d $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 04, 2021 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized (in shares)			100,000,000	100,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.000001	$ 0.000001
Common stock, shares issued (in shares)			42,457,471	42,196,296
Common stock, shares outstanding (in shares)			42,457,471	42,196,296
Outstanding pre-funded warrants (in shares)			12,663,010	12,663,010
Class of Warrant or Right, Notice Period | d			61
Exercise price (in dollars per share) | $ / shares			$ 0.000001
Proceeds from issuance of common stock | $		$ 71,300	$ 0	$ 71,675
Public offering | $		$ 4,900
Preferred stock, shares authorized (in shares)			5,000,000	5,000,000
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.000001	$ 0.000001
Preferred stock, shares issued (in shares)			0	0
Preferred stock, shares outstanding (in shares)			0	0
Options outstanding (in shares)			8,963,945	6,846,289
Options exercised (in shares)			124,928
Common stock issued upon exercise of options aggregate intrinsic value | $			$ 1,300	$ 6,000
Weighted-average grant date fair value of options granted (in dollars per share) | $ / shares			$ 6.37	$ 8.70
Stock-based compensation expense | $			$ 11,557	$ 5,622
Restricted stock units forfeited (in shares)			25,000
Unrecognized stock-based compensation cost (in dollars per share) | $			$ 29,600
Unrecognized stock-based compensation cost, weighted-average period recognized (in years)			2 years 10 months 2 days
Proceeds from ESPP | $			$ 372	$ 199
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares of common stock that may be issued (in shares)			11,264,787
Shares of common stock reserved for issuance percentage			4.00%
Award expiration period (in years)			10 years
Shares available to be granted (in shares)			5,040,300	6,037,532
2014 Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized (in shares)	2,204,819
Equity Incentive Plan 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)			23,958
Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of shares under public offering (in shares)				3,262,471
Options exercised (in shares)			124,928	882,624
Issuance of shares under Employee Stock Purchase Plan (in shares)			51,747	18,352
Performance-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted (in shares)			50,000
Restricted stock units vested (in shares)			25,000
Stock-based compensation expense | $			$ 300
Pre-funded warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding pre-funded warrants (in shares)			12,663,010
Exercise price (in dollars per share) | $ / shares		$ 0.000001
Maximum percentage of outstanding stock per stockholder			9.99%
Number of common stock in prefunded warrants (in shares)		1,737,529
Pre funded warrant issued (in dollars per share) | $ / shares		$ 15.249999
Shares issuable under 2020 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of shares under public offering (in dollars per share) | $ / shares			$ 9.53
Issuance of shares under Employee Stock Purchase Plan (in shares)			22,972
Shares issuable under 2020 ESPP | 2020 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of shares under public offering (in dollars per share) | $ / shares			$ 5.33	$ 10.84
ESPP common stock reserved for issuance (in shares)			759,936
ESPP max contribution rate			15.00%
ESPP purchase price of common stock, percent of market price			85.00%
ESPP number of offerings per year | offering			2
ESPP offering period			6 months
Issuance of shares under Employee Stock Purchase Plan (in shares)			28,775	18,352
Proceeds from ESPP | $			$ 400	$ 200
Public Stock Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of shares under public offering (in shares)		3,262,471
Sale of shares under public offering (in dollars per share) | $ / shares		$ 15.25
Equity Offering Sales Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum value | $					$ 40,000