Income taxes - Deferred Tax Assets (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 1,300,000	$ 800,000	$ 3,300,000	$ 2,000,000.0
Deferred tax assets:
Net operating loss carryforwards					$ 177,987,000	$ 163,832,000
Tax credit carryforwards					79,694,000	75,624,000
Stock-based compensation					5,192,000	5,710,000
Allowance for returns					2,492,000	4,150,000
Intangible assets					5,453,000	5,384,000
Accruals and reserves					11,687,000	19,493,000
Total deferred tax assets					296,609,000	290,795,000
Valuation allowance					(287,276,000)	(277,693,000)
Total deferred tax assets, net of valuation allowance					$ 9,333,000	$ 13,102,000