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Long-term debt: (Details) $ in Thousands, € in Millions							1 Months Ended									12 Months Ended
	Jun. 15, 2024	Jun. 11, 2024 USD ($)	May 02, 2024 USD ($)	Jun. 22, 2022 USD ($)	Jun. 22, 2022 EUR (€)	May 07, 2021 USD ($)	Dec. 31, 2024 USD ($)	Nov. 30, 2024 USD ($)	May 31, 2024 USD ($)	Nov. 30, 2023 USD ($)	May 31, 2023 USD ($)	Nov. 30, 2022 USD ($)	May 31, 2022 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2024 EUR (€)	Jun. 30, 2022 EUR (€)	Jun. 30, 2020 EUR (€)	Jun. 30, 2019 EUR (€)
Long-term debt
Interest rate (as a percent)							5.00%									5.00%			5.00%
Lease payments																	$ 77,362	$ 45,472
Redemption price percentage				101.094%	101.094%
Debt Instrument, Basis Spread on Variable Rate																3.40%
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]																us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Interest rate swap
Long-term debt
Face amount							$ 22,300									$ 22,300	38,700
Net liability, prepaid expenses							18,300									18,300	21,600
Net liability, other long term							4,000									4,000	17,100
Unrealized gains (losses)																$ 23,400	23,400
Interest rate (as a percent)																3.50%
Interest rate swap | Cash
Long-term debt
Margin deposits							22,300									$ 22,300
Interest rate swap | Unrestricted cash
Long-term debt
Margin deposits							1,100									1,100
2027 Mirror Notes
Long-term debt
Face amount		$ 300,000					300,000									$ 300,000
Proceeds from issuance of secured debt							$ 291,900
Percentage of face value							98.50%									98.50%			98.50%
Lease payments							$ 114,600
Minimum percentage of principal amount entitled for redemption		90.00%
2027 Mirror Notes | Minimum
Long-term debt
Percentage of principal amount considered as default debt		25.00%
2027 Mirror Notes | Redemption of some or all the notes
Long-term debt
Redemption price percentage of principal amount redeemed	103.50%
2027 Mirror Notes | If certain events have occurred
Long-term debt
Repurchase price, percentage		101.00%
2027 Mirror Notes | If certain events have not occurred
Long-term debt
Repurchase price in cash, percentage		100.00%
2027 Notes
Long-term debt
Face amount				$ 450,000			$ 450,000									$ 450,000
Interest rate (as a percent)				7.00%			7.00%									7.00%			7.00%
Proceeds from issuance of secured debt																$ 446,000
Debt costs																1,300
Discount on issuance of debt																$ 2,700
2027 Notes | June 15, 2024 to June 14, 2025
Long-term debt
Redemption price percentage of principal amount redeemed																103.50%
2026 Notes
Long-term debt
Face amount						$ 500,000	$ 500,000									$ 500,000
Interest rate (as a percent)							3.50%									3.50%			3.50%
Debt costs						1,300
Redemption price percentage of principal amount redeemed																100.00%
Net proceeds						496,900
Discount on issuance of debt						$ 1,800
Secured IPv4 notes
Long-term debt
Face amount			$ 206,000				$ 206,000									$ 206,000
Interest rate (as a percent)							7.924%									7.924%			7.924%
Proceeds from issuance of secured debt			$ 198,400													$ 198,426
Debt costs																$ 7,600
Maturity date			May 31, 2054
Additional interest accrued on percentage of principal amount			5.00%
Senior Unsecured 2024 Notes
Long-term debt
Face amount | €																			€ 350.0	€ 350.0	€ 215.0	€ 135.0
Interest rate (as a percent)																					4.375%
Redemption price percentage				101.094%	101.094%
Net proceeds														$ 240,300	$ 152,100
Gain on foreign exchange																	31,600	32,500
Aggregate principal amount of redemption | €					350.0
Redemption value				$ 375,200	€ 353.8
Repayments of interest				8,100	7.7
Total repayment				383,400	€ 361.5
Loss on extinguishment & redemption of 2022 notes				$ 11,900
Debt fair value																	$ 365,800	397,000
2024 Notes
Long-term debt
Interest rate (as a percent)																				4.375%
Gain (loss) on foreign exchange																		$ 31,600
Installment One | Interest rate swap
Long-term debt
Net proceeds													$ 2,100
Payment made to counter party									$ 24,200
Installment Two | Interest rate swap
Long-term debt
Net proceeds								$ 24,200		$ 21,500		$ 2,100
Payment made to counter party											$ 21,500

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