Revenue from Contracts with Customers (Capitalized Contract Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract costs capitalized during the period	$ 51,891	$ 66,607	$ 55,664
Costs amortized during the period	(58,855)	(57,741)	(49,284)
Change in capitalized contract cost, other	307	843	(1,112)
Balance of costs to obtain a contract	$ 24,363	$ 31,020	$ 21,311	$ 16,043