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Segment information: (Details) $ in Thousands	3 Months Ended		6 Months Ended
Segment information: (Details) $ in Thousands	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Geographic information
Number of operating segments \| segment			1
Revenues	$ 147,879	$ 140,990	$ 294,656	$ 281,904
Long-lived assets, net	436,010		436,010		$ 430,351
On-net
Geographic information
Revenues	111,041	103,800	220,989	207,256
Off-net
Geographic information
Revenues	36,699	37,044	73,422	74,364
Non-core
Geographic information
Revenues	139	146	245	284
North America
Geographic information
Revenues	117,140	115,131	233,537	230,745
Long-lived assets, net	308,574		308,574		306,652
North America \| On-net
Geographic information
Revenues	85,123	82,402	169,589	164,948
North America \| Off-net
Geographic information
Revenues	31,892	32,592	63,735	65,533
North America \| Non-core
Geographic information
Revenues	125	137	213	264
Europe
Geographic information
Revenues	26,880	23,573	53,910	46,847
Europe \| On-net
Geographic information
Revenues	22,372	19,348	44,792	38,468
Europe \| Off-net
Geographic information
Revenues	4,494	4,216	9,086	8,359
Europe \| Non-core
Geographic information
Revenues	14	9	32	20
Latin America
Geographic information
Revenues	1,054	436	1,882	766
Latin America \| On-net
Geographic information
Revenues	1,005	426	1,817	746
Latin America \| Off-net
Geographic information
Revenues	49	10	65	20
Asia Pacific
Geographic information
Revenues	2,712	1,850	5,156	3,546
Asia Pacific \| On-net
Geographic information
Revenues	2,449	1,624	4,622	3,094
Asia Pacific \| Off-net
Geographic information
Revenues	263	$ 226	534	$ 452
Europe and other
Geographic information
Long-lived assets, net	127,436		127,436		$ 123,699
Africa
Geographic information
Revenues	93		171
Africa \| On-net
Geographic information
Revenues	92		169
Africa \| Off-net
Geographic information
Revenues	$ 1		$ 2