Description of the business and recent developments: Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 01, 2019
Finance leases-fiber lease agreements
Additional finance lease future payments due	$ 17,600		$ 17,600
Cash paid for amounts included in the measurement of lease liabilities
Finance lease cost Amortization of right-of-use assets	4,973	$ 4,917	9,735	$ 9,888
Interest expense on finance lease liabilities	4,517	4,415	8,990	8,816
Operating lease cost	4,405	3,486	8,592	6,780
Total lease costs	$ 13,895	$ 12,818	27,317	25,484
Operating cash flows from finance leases			(8,985)	(8,827)
Operating cash flows from operating leases			(9,149)	(6,780)
Financing cash flows from finance leases			(9,883)	(5,006)
Right-of-use assets obtained in exchange for new finance lease liabilities			42,359	8,562
Right-of-use assets obtained in exchange for new operating lease liabilities			$ 20,694	$ 1,457
Weighted-average remaining lease term - finance leases (in years)	12 years 1 month 6 days	14 years 7 months 6 days	12 years 1 month 6 days	14 years 7 months 6 days
Weighted-average remaining lease term - operating leases (in years)	20 years 4 months 24 days	22 years 3 months 18 days	20 years 4 months 24 days	22 years 3 months 18 days
Weighted average discount rate - finance leases	10.80%	10.60%	10.80%	10.60%
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	$ 32,568		$ 32,568
2022	31,800		31,800
2023	30,772		30,772
2024	30,051		30,051
2025	29,710		29,710
Thereafter	214,604		214,604
Total minimum finance lease obligations	369,505		369,505
Less-amounts representing interest	(165,727)		(165,727)
Present value of minimum finance lease obligations	203,778		203,778
Current maturities, finance lease obligations	(14,734)		(14,734)		$ (8,154)
Finance lease obligations, net of current maturities	189,044		189,044		161,635
Future minimum payments under these operating lease agreements
2021	16,725		16,725
2022	16,108		16,108
2023	14,918		14,918
2024	13,833		13,833
2025	12,097		12,097
Thereafter	101,672		101,672
Total minimum operating lease obligations	175,353		175,353
Less-amounts representing interest	(64,910)		(64,910)
Present value of minimum operating lease obligations	110,443		110,443
Current maturities, operating lease liabilities	(11,292)		(11,292)		(10,101)
Lease obligations, net of current maturities	$ 99,151		$ 99,151		$ 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