Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued earnouts	$ 3,832	$ 8,819	$ 3,832	$ 8,819	$ 7,230	$ 15,086
Performance targets, maximum potential obligation	5,400		5,400		10,200
Impairment charge recognized, related to long-lived assets, additions	6,673		14,138
Other disposal costs	2		82
Asset impairment and decommission costs	2,305	63,353	23,180	74,185
Certificate of deposits					500
Treasury securities	200		200		200
Held-to-maturity investments, carrying value	900		900		800
Held-to-maturity investments, fair value	900		900		$ 900
Not Identified by Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairment and decommission costs			2,345
Write-offs relating to long-lived assets and intangibles	1,008	1,361	4,130	4,290
Former Corporate Headquarters Building [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-offs relating to long-lived assets and intangibles			$ 2,346	1,154
Revolving Credit Facility [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate			1.375%
Revolving Credit Facility [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate			2.00%
Fiber Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-offs relating to long-lived assets and intangibles		56,733		56,733
Decommissioned Towers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-offs relating to long-lived assets and intangibles	$ 3,587	$ 5,259	$ 11,449	$ 12,008