Fair value measurements - Narrative (Details)	Sep. 30, 2021
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage revenue bonds, measurement input	0.0206

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.

No definition available.

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