Goodwill and Intangible Assets - Components of Finite-Lived Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	$ 4.7	$ 4.7
Accumulated amortization	(3.7)	(3.1)
Net carrying value	1.0	1.6
Contractual and Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	4.1	4.1
Accumulated amortization	(3.2)	(2.6)
Net carrying value	0.9	1.5
Developed Technology
Finite-Lived Intangible Assets [Line Items]
Gross carrying value	0.6	0.6
Accumulated amortization	(0.5)	(0.5)
Net carrying value	$ 0.1	$ 0.1