Description of Business and Summary of Significant Accounting Policies - Deferred Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	$ 55,015	$ 55,015	$ 35,563
Total deferred revenue - long term	222	$ 222	0
Hosted Services - Business
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	52,232		27,011
Total deferred revenue - long term	19		0
Professional Services
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	2,783		8,552
Total deferred revenue - long term	$ 203		$ 0