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Geographic information: (Details) $ in Thousands	12 Months Ended
Geographic information: (Details) $ in Thousands	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Geographic information
Number of operating segments \| segment	1
Revenues	$ 589,797	$ 568,103	$ 546,159
Long-lived assets, net	457,892	430,351
On-net
Geographic information
Revenues	442,838	419,454	396,753
Off-net
Geographic information
Revenues	146,383	148,128	148,931
Non-core
Geographic information
Revenues	576	521	475
North America
Geographic information
Revenues	467,992	461,277	451,567
Long-lived assets, net	331,537	306,652
North America \| On-net
Geographic information
Revenues	340,107	330,924	319,330
North America \| Off-net
Geographic information
Revenues	127,383	129,879	131,815
North America \| Non-core
Geographic information
Revenues	502	474	422
Europe
Geographic information
Revenues	105,730	96,867	88,696
Europe \| On-net
Geographic information
Revenues	87,929	79,568	72,320
Europe \| Off-net
Geographic information
Revenues	17,729	17,252	16,323
Europe \| Non-core
Geographic information
Revenues	72	47	53
Asia Pacific
Geographic information
Revenues	11,292	7,783	5,393
Asia Pacific \| On-net
Geographic information
Revenues	10,197	6,834	4,615
Asia Pacific \| Off-net
Geographic information
Revenues	1,094	949	778
Asia Pacific \| Non-core
Geographic information
Revenues	1
Europe and other
Geographic information
Long-lived assets, net	126,355	123,699
Africa
Geographic information
Revenues	507	72
Africa \| On-net
Geographic information
Revenues	503	72
Africa \| Off-net
Geographic information
Revenues	4
South America
Geographic information
Revenues	4,276	2,104	503
South America \| On-net
Geographic information
Revenues	4,102	2,056	488
South America \| Off-net
Geographic information
Revenues	173	$ 48	$ 15
South America \| Non-core
Geographic information
Revenues	$ 1