Employee benefit plans - Nonqualified retirement plan (Details) - Nonqualified retirement plan - USD ($) $ in Thousands	12 Months Ended
Mar. 28, 2020	Mar. 30, 2019	Mar. 31, 2018
Pension plans
Matching contribution	$ 0	$ 0	$ 0
Other current assets
Pension plans
Fair value of the plan asset	5,066	5,810
Accrued liabilities
Pension plans
Carrying value of the plan liability	$ 5,070	$ 5,816

Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant