Income taxes - Narrative (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components Of Income Tax Expense Benefit [Line Items]
Income tax expense (benefit)	$ 258,000	$ 686,000	$ (545,000)
Income tax expense, discontinued operations	$ 0	$ 0	$ 0
Effective income tax rate	0.00%	(0.10%)	0.10%
Approximately valuation allowance increased	$ 183,400,000
Operating loss carryforwards, without expiration dates	1,920,000,000
Operating loss carryforwards, with expiration dates	711,000,000
Income tax examination, penalties and interest accrued	$ 0	$ 0	$ 0
Research Tax Credit Carryforward
Components Of Income Tax Expense Benefit [Line Items]
Limitations on use of net operating losses and tax credit carryforwards, period	3 years
Limitations on use of net operating losses and tax credit carryforwards, percentage	50.00%
U.S.
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards	$ 2,630,000,000	2,030,000,000.00	1,620,000,000
U.S. | Research Tax Credit Carryforward
Components Of Income Tax Expense Benefit [Line Items]
Tax credit carryforward amount	268,300,000	235,300,000	203,100,000
State and Local Jurisdiction
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards	2,390,000,000	1,890,000,000	1,560,000,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Components Of Income Tax Expense Benefit [Line Items]
Tax credit carryforward amount	$ 16,900,000	$ 14,500,000	$ 13,600,000