Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Remaining performance obligation	$ 1,500.0
Remaining performance obligation, percent to be recognized as revenue within one year	50.00%
Long-term contract assets	$ 6.0
Revenue recognized, previously included in deferred revenue		$ 104.6
Deferred sales commission	10.1	11.0
Amortization expense related to deferred commissions	1.7
Cost to fulfill contract, net	77.1	$ 76.0
Amortization of costs to fulfill contracts	$ 3.6