Income Taxes - Schedule of Changes in Amount of Uncertain Tax Positions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unrecognized liabilities:
Balance at the beginning of the period	$ 7.3	$ 7.3	$ 12.2
Change in federal tax rate	0.0	0.0	(4.9)
Balance at the end of the period	$ 7.3	$ 7.3	$ 7.3