Summary of Significant Accounting Policies - Concentration of Credit Risk and Significant Customers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in the allowance for doubtful accounts
Balance at Beginning of Year	$ 4,649	$ 3,115	$ 2,323
Additions: Charged to Operations	1,284	1,255	1,688
Additions: Charged to Deferred Revenue	1,306	1,177	194
Less: Write-offs	1,043	898	1,090
Balance at End of Year	$ 6,196	$ 4,649	$ 3,115