Fair Value Measurements (Summary of Asset Impairment and Decommission Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurements [Abstract]
Asset impairment	$ 18,794	$ 14,350	$ 15,389
Write-off of carrying value of decommissioned towers	11,155	10,795	16,861
Other (including third party decommission costs)	3,154	1,989	4,447
Total asset impairment and decommission costs	$ 33,103	$ 27,134	$ 36,697