Income taxes: - Effective income tax rate reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Reconciliation of the Federal statutory income taxes to the amounts reported in the financial statements
Federal income tax expense at statutory rates	$ 51,476	$ 54,381	$ (256,086)
State income taxes, net of federal benefit	$ 17,114	1,587	3,722
Effective Income Tax Rate Reconciliation, State and Local Jurisdiction, Contribution Greater than 50 Percent, Tax Effect [Extensible Enumeration]	CALIFORNIA, stpr:IL, stpr:KS
Impact of foreign operations	$ (2,004)	(1,602)	868
Effect of cross-border tax laws	(1,565)
Non-deductible expenses	(2,230)	(2,713)	(2,783)
Bargain purchase gain - Cogent Fiber Business acquisition		4,662	295,351
Tax effect of TCJA from foreign earnings			(490)
Changes in valuation allowance		(740)	13,382
Income tax benefit (expense)	$ 62,791	$ 55,575	$ 53,964
Effective income tax rate reconciliation (as a percent)
Benefit for income taxes at U.S. federal statutory rate (as a percent)	21.00%
U.S. State and local income taxes, net of federal benefit (as a percent)	7.10%
Foreign tax effects (as a percent)	(0.50%)
Effect of cross-border tax laws (as a percent)	(1.00%)
Non-deductible expenses (as a percent)	(1.00%)
Effective income tax rate (as a percent)	25.60%

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to the acquisition of business.

No definition available.