Fair Value Measurements (Summary of Asset Impairment and Decommission Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurements [Abstract]
Asset impairment	$ 31,552	$ 18,794	$ 14,350
Write-off of carrying value of decommissioned towers	7,456	11,155	10,795
Other (including third party decommission costs)	1,089	3,154	1,989
Total asset impairment and decommission costs	$ 40,097	$ 33,103	$ 27,134