Disclosure - Goodwill and Other Intangible Assets - Summary of Intangible Assets Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Cost amortizable intangible assets	$ 8.1	$ 8.1
Accumulated amortization intangible assets	4.2	2.9
Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Cost amortizable intangible assets	4.9	4.9
Accumulated amortization intangible assets	1.8	1.5
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Cost amortizable intangible assets	1.6	1.6
Accumulated amortization intangible assets	0.9	0.5
Other [Member]
Finite Lived Intangible Assets [Line Items]
Cost amortizable intangible assets	1.6	1.6
Accumulated amortization intangible assets	$ 1.5	$ 0.9