Revenue, Deferred Revenue And Deferred Commissions - Deferred Revenues (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Contract With Customer, Asset And Liability [Roll Forward]
December 31, 2017	$ 32,477
Additions	5,191	$ 2,561
June 30, 2018	33,410
Accounting Standards Update 2014-09
Contract With Customer, Asset And Liability [Roll Forward]
Additions	30,976
Revenue recognized	(30,043)
ASC 606 | Accounting Standards Update 2014-09
Contract With Customer, Asset And Liability [Roll Forward]
December 31, 2017	(4,200)
June 30, 2018	$ (4,200)