Credit agreement and changes in debt - HEI private placement (Details) - Senior Notes	Mar. 31, 2023 USD ($)
Series 2023A
Debt Instrument [Line Items]
Aggregate principal amount	$ 39,000,000
Fixed coupon interest rate	6.04%
Series 2023B
Debt Instrument [Line Items]
Aggregate principal amount	$ 61,000,000
Fixed coupon interest rate	6.10%

Face (par) amount of debt instrument at time of issuance.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant