Common stock and preferred stock - Summary of Future Issuance of Common Stock Shares (Detail) - shares shares in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	10,369	8,764
2013 Stock Option and Incentive Plan
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	2,545	2,007
2013 Employee Stock Purchase Plan
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	67	147
Options to purchase common stock
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	6,262	5,483
Restricted stock units
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	1,495	1,127