Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Components Of Income Tax Expense Benefit [Line Items]
Income tax effective rate	50.70%		242.80%
Income tax expense (benefit) impact of the tax act	$ (0.5)	$ 8.3
Minimum [Member]
Components Of Income Tax Expense Benefit [Line Items]
Decrease in unrecognized tax benefits	2.1
Maximum [Member]
Components Of Income Tax Expense Benefit [Line Items]
Decrease in unrecognized tax benefits	$ 4.1