Description of the business and recent developments: Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jan. 01, 2019
Finance leases-fiber lease agreements
Additional finance lease future payments due	$ 20,700		$ 20,700
Cash paid for amounts included in the measurement of lease liabilities
Finance lease cost Amortization of right-of-use assets	6,382	$ 4,963	16,117	$ 14,851
Interest expense on finance lease liabilities	4,804	4,414	13,794	13,230
Operating lease cost	4,269	3,716	12,860	10,497
Total lease costs	$ 15,455	$ 13,093	42,771	38,578
Operating cash flows from finance leases			(14,150)	(12,957)
Operating cash flows from operating leases			(13,785)	(8,443)
Financing cash flows from finance leases			(19,392)	(7,035)
Right-of-use assets obtained in exchange for new finance lease liabilities			61,504	11,342
Right-of-use assets obtained in exchange for new operating lease liabilities			$ 24,866	$ 6,912
Weighted-average remaining lease term - finance leases (in years)	12 years 3 months 18 days	14 years 6 months	12 years 3 months 18 days	14 years 6 months
Weighted-average remaining lease term - operating leases (in years)	20 years 4 months 24 days	21 years 8 months 12 days	20 years 4 months 24 days	21 years 8 months 12 days
Weighted average discount rate - finance leases	10.50%	10.50%	10.50%	10.50%
Weighted average discount rate - operating leases	5.40%	5.70%	5.40%	5.70%
Future minimum payments (principal and interest) under these finance leases
2021	$ 33,471		$ 33,471
2022	32,638		32,638
2023	31,650		31,650
2024	31,753		31,753
2025	28,495		28,495
Thereafter	225,320		225,320
Total minimum finance lease obligations	383,327		383,327
Less-amounts representing interest	(170,387)		(170,387)
Present value of minimum finance lease obligations	212,940		212,940
Current maturities, finance lease obligations	(15,252)		(15,252)		$ (8,154)
Finance lease obligations, net of current maturities	197,688		197,688		161,635
Future minimum payments under these operating lease agreements
2021	17,579		17,579
2022	16,535		16,535
2023	15,674		15,674
2024	14,198		14,198
2025	12,124		12,124
Thereafter	103,809		103,809
Total minimum operating lease obligations	179,919		179,919
Less-amounts representing interest	(66,466)		(66,466)
Present value of minimum operating lease obligations	113,453		113,453
Current maturities, operating lease liabilities	(12,006)		(12,006)		(10,101)
Lease obligations, net of current maturities	$ 101,447		$ 101,447		$ 86,690
Asset and lease liability						$ 97,300
Minimum
Finance leases-fiber lease agreements
Initial terms	15 years		15 years
Maximum
Finance leases-fiber lease agreements
Initial terms	20 years		20 years