Long-term debt - Narrative (Details)	3 Months Ended
	Mar. 31, 2025 USD ($) Covenant	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Cash and cash equivalents	$ 716,647,000	$ 693,214,000
Number of covenants | Covenant	1
Amended and Restated Competitive Advance and Revolving Credit Agreement | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Unused borrowing capacity	$ 738,200,000
Maximum borrowing capacity under credit facility	$ 750,000,000
Line of credit facility, expiration date	Jan. 31, 2029
Amended and Restated Competitive Advance and Revolving Credit Agreement | Line of Credit | Letter of Credit
Debt Instrument [Line Items]
Current borrowing capacity under credit facility	$ 11,800,000