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Fair value measurements - Narrative (Details) $ in Millions | Aug. 04, 2018 USD ($)
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Fair Value Disclosures [Abstract] |
Deferred payment, fair value disclosure | $ 17.1

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- Definition Deferred Payment, Fair Value Disclosure + References No definition available. + Details
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Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration