Description of the business and recent developments: (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($) MB	Dec. 31, 2014 USD ($)
Financial instruments
Senior unsecured notes	$ 200,000	$ 200,000
Senior secured notes	250,000
Letters of credit, outstanding amount	$ 400
Minimum
On-net service - high-speed Internet access and IP connectivity
Speed per second of bandwidth (in megabits) | MB	100
Maximum
On-net service - high-speed Internet access and IP connectivity
Speed per second of bandwidth (in megabits) | MB	10,240
Senior unsecured notes
Financial instruments
Senior unsecured notes	$ 200,000
Senior unsecured notes | Level 2
Financial instruments
Debt instrument, fair value amount	190,800
Senior secured notes
Financial instruments
Senior secured notes	250,000
Senior secured notes | Level 2
Financial instruments
Debt instrument, fair value amount	$ 247,500