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Long-term debt: (Details) - USD ($) $ in Thousands						1 Months Ended					3 Months Ended	6 Months Ended		9 Months Ended
	Jun. 04, 2025	Apr. 11, 2025	Jun. 15, 2024	Jun. 11, 2024	May 02, 2024	May 31, 2025	Nov. 30, 2024	Jun. 30, 2024	May 31, 2024	Jun. 30, 2022	Sep. 30, 2025	Oct. 31, 2024	Apr. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Jun. 17, 2025	Dec. 31, 2024
Long-term debt
Proceeds from issuance of secured debt		$ 170,500
Loss on debt extinguishment and redemption - 2026 notes	$ 5,600													$ 5,606
Lease payments														25,314	$ 46,653
Debt Instrument, Restricted Value		72,600
Debt Instrument, Unrestricted Value		$ 97,900
Interest rate swap
Long-term debt
Fair value of interest rate swaps											$ 13,800			13,800			$ 4,000
Interest rate swap | Restricted cash
Long-term debt
Margin deposits											13,800			13,800
Interest rate swap | Unrestricted cash
Long-term debt
Margin deposits											500			500
Interest rate swap | Accrued and other current liabilities
Long-term debt
Fair value of interest rate swaps											22,300			22,300			14,300
Interest rate swap | Other long-term liabilities
Long-term debt
Fair value of interest rate swaps											18,300			$ 18,300			$ 14,300
SOFR | Interest rate swap
Long-term debt
Interest rate (as a percent)														3.50%
Payment of debt in Installments						$ 9,700	$ 12,100
Net proceeds						$ 9,700						$ 12,100	$ 12,100
Payment made to counter party									$ 12,100
2027 Mirror Notes
Long-term debt
Face amount				$ 300,000				$ 300,000			$ 300,000			$ 300,000
Interest rate (as a percent)				7.00%				7.00%
Proceeds from issuance of secured debt														$ 291,900
Percentage of face value											98.50%			98.50%
Lease payments														$ 114,600
Maturity date				Jun. 15, 2027				Jun. 15, 2027
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%
Maturity date										Jun. 15, 2027
2026 Notes
Long-term debt
Interest rate (as a percent)											3.50%			3.50%
Aggregate Principal amount	500,000
Amount of net proceeds from offering	507,300
Amount of settlement payment	5,000
Amount of accrued interest redeemed	$ 2,200
Redemption value														$ 500,000
Secured IPv4 notes
Long-term debt
Proceeds from issuance of secured debt														170,479	198,426
Debt costs														4,000	$ 7,600
Secured IPv4 Notes
Long-term debt
Face amount					$ 380,400
Senior secured 2032 notes
Long-term debt
Face amount											$ 600,000			$ 600,000		$ 600,000
Interest rate (as a percent)											6.50%			6.50%		6.50%
Proceeds from issuance of secured debt														$ 597,842
Debt costs														$ 2,200
Repurchase price in cash, percentage														100.00%
Minimum percentage of principal amount entitled for redemption														90.00%
Senior secured 2032 notes | Minimum
Long-term debt
Percentage of principal amount considered as default debt											25.00%			25.00%
Senior secured 2032 notes | Redemption of some or all the notes
Long-term debt
Repurchase price, percentage														100.00%
Senior secured 2032 notes | Issuers may redeem up to 40% of notes
Long-term debt
Redemption price percentage														106.50%
Repurchase price, percentage														40.00%
Senior secured 2032 notes | Redemption after July 1, 2028
Long-term debt
Repurchase price, percentage														103.25%
Senior secured 2032 notes | Change in control accompanied by certain rating events
Long-term debt
Repurchase price, percentage														101.00%
Existing 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
Maturity date					May 31, 2054
Percentage Of Noteholders Voting Rights To Amend Covenants		50.00%
Additional interest accrued on percentage of principal amount					5.00%
Existing IPv4 Notes | Base Rate [Member]
Long-term debt
Debt Instrument, Basis Spread on Variable Rate														5.00%
Existing IPv4 Notes | US Treasury (UST) Interest Rate [Member]
Long-term debt
Debt Instrument, Basis Spread on Variable Rate														3.40%
IPv4 New Notes
Long-term debt
Face amount		$ 174,400									$ 174,400			$ 174,400
Interest rate (as a percent)		6.646%									6.646%			6.646%
Maturity date		Apr. 30, 2055
Restriction on restricted cash											$ 14,100
Additional interest accrued on percentage of principal amount		5.00%
IPv4 New Notes | Base Rate [Member]
Long-term debt
Debt Instrument, Basis Spread on Variable Rate		5.00%
IPv4 New Notes | US Treasury (UST) Interest Rate [Member]
Long-term debt
Debt Instrument, Basis Spread on Variable Rate		3.00%

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