Segment Information (Revenue by Customer Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Major Customer [Line Items]
Revenue	$ 767,170	$ 732,901	$ 2,427,044	$ 2,200,741
Strategic Service Provider [Member]
Revenue, Major Customer [Line Items]
Revenue	21,589	38,475	71,091	84,307
Non-strategic Service Provider [Member]
Revenue, Major Customer [Line Items]
Revenue	$ 745,581	$ 694,426	$ 2,355,953	$ 2,116,434