Long-term debt - Narrative (Details) - USD ($)			3 Months Ended		9 Months Ended
	Oct. 10, 2024	Nov. 23, 2020	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 19, 2024	Dec. 31, 2023	Sep. 22, 2020
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	$ 4,700,000	$ 4,700,000
5.50% Senior Secured Notes | Secured Debt
Debt Instrument [Line Items]
Aggregate principal amount of debt issued									$ 125,000,000
Stated interest rate (as a percent)									5.50%
Issue price (as a percent)									100.00%
Long-term debt, gross				$ 113,050,000.00		$ 113,050,000.00	$ 113,050,000.00
Redemption price (as a percent)		99.80%
5.50% Senior Secured Notes | Secured Debt | Subsequent Event
Debt Instrument [Line Items]
Long-term debt, gross	$ 113,050,000.00
Redemption price (as a percent)	100.00%
6.75% Senior Secured Notes | Secured Debt
Debt Instrument [Line Items]
Stated interest rate (as a percent)									6.75%
Long-term debt, gross									$ 150,000,000
Long term debt held in treasury									1,400,000
Long term debt outstanding, net of amount held in treasury									$ 148,600,000