Long-Term Debt - Summary of Debt Refinancing Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred finance costs, gross	$ 2.7	$ 2.7
Accumulated amortization,Beginning Balance	(1.1)	(0.5)
Amortization in the year	(0.7)	(0.6)	$ (0.4)
Accumulated amortization,Ending balance	(1.8)	(1.1)	$ (0.5)
Deferred finance costs, net	$ 0.9	$ 1.6