Bank borrowings - Accounts Receivable Factoring Agreement (Details) - Secured Debt - Accounts Receivable Factoring Agreement August Ninth Two Thousand Nineteen - USD ($)		12 Months Ended
	Aug. 09, 2019	Jun. 30, 2020
Debt Instrument [Line Items]
Accounts Receivable Factoring Agreement, maximum borrowing capacity, percent of net accounts receivable	70.00%
Accounts Receivable Factoring Agreement, maximum borrowing capacity	$ 30,000,000.0
Basis spread on variable rate	1.75%
Proceeds from Accounts Receivable Factoring Agreement		$ 20,000,000.0
Repayments of Accounts Receivable Factoring Agreement		20,000,000
Accounts Receivable Factoring Agreement, borrowed amount outstanding		0
Accounts Receivable Factoring Agreement, remaining borrowing capacity		$ 30,000,000.0