Income taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of beginning of period	$ 15,945	$ 12,095
Increases (decreases) for tax positions related to current period	3,149	3,554
Increases (decreases) for tax positions related to prior periods	(100)	(296)
Balance as of end of period	$ 18,994	$ 15,945