Stock-based compensation - Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 22,337	$ 11,552	$ 40,405	$ 18,575
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	1,241	731	2,119	1,218
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	4,838	2,427	8,865	4,428
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 16,258	$ 8,394	$ 29,421	$ 12,929