Income taxes - Schedule of Effective Income Tax Rate Reconciliation (Parenthetical) (Detail) - CNY (¥) ¥ in Thousands	12 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Super deduction for research and development expenses	¥ 1,881	¥ 2,632	¥ 4,719
Tax Year 2018 [Member]
Effective income tax rate reconciliation non-deductible expense research and development percentage	175.00%
Effective income tax rate reconciliation non-deductible expense research and development additional deduction percentage	75.00%

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible research and development expense.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

Name:	us-gaap_IncomeTaxReconciliationNondeductibleExpenseResearchAndDevelopment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration