Revenue Recognition (Deferred Revenue) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	$ 66,210	$ 55,015
Total deferred revenue - long term	177	222
Hosted Services - Business
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	61,463	52,232
Total deferred revenue - long term	4	19
Professional Services
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	4,747	2,783
Total deferred revenue - long term	$ 173	$ 203