Deferred Costs - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Deferred sales commissions	$ 33.0		$ 33.0		$ 29.1
Deferred costs capitalized	5.4	$ 4.5	13.6	$ 10.6
Acquisition related costs			2.7
Amortization expense for deferred costs	$ 4.3	$ 3.5	$ 12.2	$ 10.1