Revenues - (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract with customer, asset	$ 0	$ 0
Deferred revenues	463,900,000	$ 385,100,000
Increase in contract liabilities	78,800,000
Billings paid in advance	338,200,000
Revenue recognized	259,400,000
Revenue, remaining performance obligation	$ 463,900,000
Revenue, remaining performance obligation, current, percentage	99.00%	99.00%
Deferred commissions	$ 58,500,000	$ 49,500,000