Property and equipment: (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property and equipment
Property and equipment, gross	$ 1,619,515	$ 1,515,867
Accumulated depreciation and amortization	(1,161,635)	(1,085,532)
Total property and equipment, net	457,880	430,335
Depreciation and amortization	89,240	83,477	$ 80,247
Owned assets
Property and equipment
Property and equipment, gross	1,095,040	1,032,889
Accumulated depreciation and amortization	(912,579)	(856,859)
Total property and equipment, net	182,461	176,030
Network equipment \| Owned assets
Property and equipment
Property and equipment, gross	650,634	611,265
Leasehold improvements \| Owned assets
Property and equipment
Property and equipment, gross	250,623	241,379
System infrastructure \| Owned assets
Property and equipment
Property and equipment, gross	160,376	148,533
Capitalized salaries and related benefits of employees	13,400	12,100	$ 10,700
Software \| Owned assets
Property and equipment
Property and equipment, gross	11,028	10,609
Office and other equipment \| Owned assets
Property and equipment
Property and equipment, gross	20,999	19,611
Owned buildings \| Owned assets
Property and equipment
Property and equipment, gross	1,273	1,376
Land \| Owned assets
Property and equipment
Property and equipment, gross	107	116
Indefeasible rights of use (IRUs)
Property and equipment
Property and equipment, gross	524,475	482,978
Accumulated depreciation and amortization	(249,056)	(228,673)
Total property and equipment, net	$ 275,419	$ 254,305

Represents the compensation costs the entity capitalizes as a part of property, plant and equipment.

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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