Description of the business and recent developments: Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Finance leases-fiber lease agreements
Additional finance lease future payments due	$ 35,100		$ 35,100
Cash paid for amounts included in the measurement of lease liabilities
Finance lease cost, Amortization of right-of-use assets	6,847	$ 6,382	19,571	$ 16,117
Interest expense on finance lease liabilities	4,977	4,804	14,888	13,794
Operating lease cost	4,572	4,269	13,660	12,860
Total lease costs	$ 16,396	$ 15,455	48,119	42,771
Operating cash flows from finance leases			(12,694)	(14,150)
Operating cash flows from operating leases			(14,077)	(13,785)
Financing cash flows from finance leases			(16,826)	(19,392)
Right-of-use assets obtained in exchange for new finance lease liabilities			38,411	61,504
Right-of-use assets obtained in exchange for new operating lease liabilities			$ 15,732	$ 24,866
Weighted-average remaining lease term - finance leases (in years)	12 years 7 months 6 days	12 years 3 months 18 days	12 years 7 months 6 days	12 years 3 months 18 days
Weighted-average remaining lease term - operating leases (in years)	19 years 2 months 12 days	20 years 4 months 24 days	19 years 2 months 12 days	20 years 4 months 24 days
Weighted average discount rate - finance leases	9.30%	10.50%	9.30%	10.50%
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	$ 35,675		$ 35,675
2023	34,812		34,812
2024	34,997		34,997
2025	31,738		31,738
2026	26,829		26,829
Thereafter	248,490		248,490
Total minimum lease obligations	412,541		412,541
Less-amounts representing interest	(173,002)		(173,002)
Present value of minimum lease obligations	239,539		239,539
Current maturities	(16,685)		(16,685)		$ (15,702)
Finance lease obligations, net of current maturities	222,854		222,854		203,438
Future minimum payments under these operating lease agreements
2022	17,802		17,802
2023	18,295		18,295
2024	17,243		17,243
2025	15,228		15,228
2026	13,116		13,116
Thereafter	115,788		115,788
Total minimum lease obligations	197,472		197,472
Less-amounts representing interest	(71,095)		(71,095)
Present value of minimum lease obligations	126,377		126,377
Current maturities	(11,312)		(11,312)		(11,151)
Lease obligations, net of current maturities	$ 115,065		$ 115,065		$ 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