Long-term debt - Narrative (Details) - 5.50% Senior Secured Notes - USD ($)		3 Months Ended		9 Months Ended
	Nov. 23, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2023	Sep. 22, 2020
Debt Instrument [Line Items]
Interest expense		$ 1,600,000	$ 1,700,000	$ 4,700,000	$ 5,200,000
Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)							5.50%
Aggregate principal amount of debt issued							$ 125,000,000
Issue price (as a percent)							100.00%
Redemption price (as a percent)	99.80%
Interest rate during period (as a percent)	5.50%
Debt issuance costs							$ 3,100,000
Debt issuance cost, amount paid to subsidiary							1,900,000
Debt issuance costs capitalized							$ 1,200,000
Debt instrument, repurchase amount						$ 1,000,000
Notes outstanding		$ 113,050,000.00		$ 113,050,000.00