Business and Summary of Significant Accounting Policies - Activity of Deferred Contract Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Capitalized Contract Cost [Roll Forward]
Beginning balance	$ 59,811	$ 50,451	$ 59,434	$ 50,176
Capitalization of contract acquisition costs	8,608	4,700	15,234	9,847
Amortization of deferred contract acquisition costs	(6,553)	(4,346)	(12,802)	(9,218)
Ending balance	$ 61,866	$ 50,805	$ 61,866	$ 50,805