Revenue Recognition - Deferred Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	$ 102,905	$ 88,848
Total deferred revenue - long term	179	409
Hosted Services - Business
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	100,694	86,144
Hosted Services - Consumer
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	883	835
Professional Services
Disaggregation of Revenue [Line Items]
Total deferred revenue - short term	1,328	1,869
Total deferred revenue - long term	$ 179	$ 409