Revenue Recognition - Summary of Activity in Deferred Sales Commissions and Deferred Deployment Costs (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Deferred Sales Commissions [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	$ 0.8	$ 1.1
Costs recognized as assets	0.1	0.3
Amortization of costs	(0.3)	(0.6)
Ending balance	0.6	0.8
Deferred Deployment Costs [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	2.9	3.1
Costs recognized as assets	0.4	0.5
Amortization of costs	(0.6)	(0.7)
Ending balance	$ 2.7	$ 2.9