Presentation, Summary of Significant Accounting Policies and Recent Accounting Standard Updates - Summary of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable
Balance, beginning of period	$ 0.2	$ 0.3
Expenses for sales returns and allowances, and uncollectible accounts, net of recoveries	0.1	(0.1)	$ 0.3
Balance, end of period	$ 0.3	$ 0.2	$ 0.3