Revenue Recognition Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 400,000								$ 400,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	18 months								18 months
Contract with Customer, Liability, Revenue Recognized									$ 456,855	$ 445,547
Total revenues	$ 309,687	$ 302,534	$ 297,584	$ 279,541	$ 273,803	$ 261,531	$ 259,875	$ 253,573	1,189,346	1,048,782	$ 1,002,286
Capitalized Contract Cost, Gross	$ 68,982				$ 49,636				68,982	49,636
Deferred Tax Liabilities, Deferred Expense, Other Capitalized Costs												$ 9,636
Amortization of deferred customer acquisition costs									11,359	10,287	0
Subscription services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues									637,980	607,823
Usage
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues									338,697	247,256
USF and others
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues									212,669	193,703
Business Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues									$ 803,880	$ 608,144	$ 498,922
Customer Life									7 years
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Performance Obligation, Description of Timing									1
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Performance Obligation, Description of Timing									3