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Fair value measurements - Narrative (Details)	Mar. 31, 2021
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage revenue bonds, measurement input	0.0207

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- Definition

Asset Backed Securities, Measurement Input

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: