Common stock and preferred stock - Summary of Future Issuance of Common Stock Shares (Detail) - shares shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	8,764	7,204
2013 Stock Option and Incentive Plan
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	2,007	1,458
Options to purchase common stock
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	5,483	4,643
Restricted stock units
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	1,127	931
2013 Employee Stock Purchase Plan
Schedule of Capitalization [Line Items]
Common shares reserved for future issuance (in shares)	147	172