Long-term debt - Narrative (Details) - USD ($)		3 Months Ended		6 Months Ended
	Nov. 23, 2020	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Mar. 31, 2023	Sep. 22, 2020
Debt Instrument [Line Items]
Debt issuance costs	$ 3,100,000
Debt issuance cost, amount paid to subsidiary	1,900,000
Debt issuance costs capitalized	$ 1,200,000
5.50% Senior Secured Notes
Debt Instrument [Line Items]
Long-term debt, gross		$ 113,050,000		$ 113,050,000		$ 113,050,000
Interest expense		1,600,000	$ 1,600,000	3,100,000	$ 3,100,000
6.75% Senior Secured Notes
Debt Instrument [Line Items]
Long term debt held in treasury								$ 1,400,000
Long term debt outstanding, net of amount held in treasury								$ 148,600,000
Senior Secured Notes | 5.50% 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 instrument, repurchase amount							$ 1,000,000
Notes outstanding		$ 113,050,000.00		$ 113,050,000.00
Senior Secured Notes | 6.75% Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate (as a percent)								6.75%
Long-term debt, gross								$ 150,000,000