Net Property and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Cash payment	$ 19,700	$ 0	$ 19,700	$ 0
Fair market value of IRU capacity	$ 14,100
Other Income (Expense)
Property, Plant and Equipment [Line Items]
Gain from adjustment to fair value			$ 3,100