Preferred units - Distributions (Details) - USD ($) $ in Thousands			3 Months Ended
	Nov. 15, 2022	Nov. 15, 2021	Oct. 31, 2022	Oct. 31, 2021
Temporary Equity [Line Items]
Quarterly distribution accrued			$ 18,000	$ 16,800
Cash distribution		$ 15,100	$ 15,580	$ 15,673
Preferred units additional quarterly distribution accrued		$ 1,700
Cash tax distribution rate			25.00%
Tax rate multiplied by estimated taxable income percentage			0.25%
Additional distribution, percentage of taxable income			20.00%
Additional distribution, divisor			0.8
Subsequent Event
Temporary Equity [Line Items]
Quarterly distribution accrued	$ 2,700
Cash distribution	$ 15,300
Minimum
Temporary Equity [Line Items]
Applicable premium distribution rate			0.75
Maximum
Temporary Equity [Line Items]
Applicable premium distribution rate			3
First Five Years After March 30, 2021 | Minimum
Temporary Equity [Line Items]
Preferred units distribution rate			8.956%
First Five Years After March 30, 2021 | Maximum
Temporary Equity [Line Items]
Preferred units distribution rate			11.125%