Income taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) ¥ in Thousands, $ in Thousands	12 Months Ended
Mar. 31, 2021 USD ($)	Mar. 31, 2021 CNY (¥)	Mar. 31, 2020 CNY (¥)	Mar. 31, 2019 CNY (¥)
Income Tax Disclosure [Abstract]
Loss before income tax	$ (29,516)	¥ (193,391)	¥ (175,925)	¥ (231,758)
Income tax computed at respective applicable tax rate		(48,348)	(43,981)	(57,940)
Effect of different tax jurisdiction		14,272	19,507	25,553
Super deduction for research and development expenses (a)		(2,632)	(4,719)	(5,969)
Non-deductible expenses		140	138	133
Change in valuation allowance		37,439	29,567	38,364
Total	$ 133	¥ 871	¥ 512	¥ 141
PRC statutory income tax rates	25.00%	25.00%	25.00%	25.00%
Effect on tax rates in different tax jurisdiction	(7.00%)	(7.00%)	(11.00%)	(11.00%)
Super deduction for research and development expenses	1.00%	1.00%	3.00%	3.00%
Non-deductible expenses	0.00%	0.00%	0.00%	0.00%
Change in valuation allowance	(19.00%)	(19.00%)	(17.00%)	(17.00%)
Total	0.00%	0.00%	0.00%	0.00%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage 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 changes in the valuation allowance for deferred tax assets.

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Percentage 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 applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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