Description of the business and recent developments: Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Finance leases-fiber lease agreements
Additional finance lease future payments due	$ 29,500		$ 29,500
Cash paid for amounts included in the measurement of lease liabilities
Finance lease cost, Amortization of right-of-use assets	6,378	$ 4,973	12,724	$ 9,735
Interest expense on finance lease liabilities	4,685	4,517	9,911	8,990
Operating lease cost	4,671	4,405	9,088	8,592
Total lease costs	$ 15,734	$ 13,895	31,723	27,317
Operating cash flows from finance leases			(10,111)	(8,985)
Operating cash flows from operating leases			(10,104)	(9,149)
Financing cash flows from finance leases			(11,936)	(9,883)
Right-of-use assets obtained in exchange for new finance lease liabilities			16,218	42,359
Right-of-use assets obtained in exchange for new operating lease liabilities			$ 12,531	$ 20,694
Weighted-average remaining lease term - finance leases (in years)	12 years 6 months	12 years 1 month 6 days	12 years 6 months	12 years 1 month 6 days
Weighted-average remaining lease term - operating leases (in years)	19 years 4 months 24 days	20 years 4 months 24 days	19 years 4 months 24 days	20 years 4 months 24 days
Weighted average discount rate - finance leases	9.80%	10.80%	9.80%	10.80%
Weighted average discount rate - operating leases	5.50%	5.40%	5.50%	5.40%
Future minimum payments (principal and interest) under these finance leases
2022	$ 34,461		$ 34,461
2023	33,569		33,569
2024	32,917		32,917
2025	32,573		32,573
2026	25,420		25,420
Thereafter	235,307		235,307
Total minimum finance lease obligations	394,247		394,247
Less-amounts representing interest	(169,655)		(169,655)
Present value of minimum finance lease obligations	224,592		224,592
Current maturities	(16,004)		(16,004)		$ (15,702)
Finance lease obligations, net of current maturities	208,588		208,588		203,438
Future minimum payments under these operating lease agreements
Current maturities	(11,783)		(11,783)		(11,151)
Lease obligations, net of current maturities	$ 115,949		$ 115,949		$ 111,318
Minimum
Finance leases-fiber lease agreements
Initial terms	15 years		15 years
Maximum
Finance leases-fiber lease agreements
Initial terms	20 years		20 years