Revenue Recognition (Deferred Revenue) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	$ 56,117	$ 35,563
Total deferred revenue - long term	2,067	0
Hosted Services - Business
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	45,225	27,011
Total deferred revenue - long term	1,653	0
Professional Services
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	10,892	8,552
Total deferred revenue - long term	$ 414	$ 0