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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Federal income tax rate	21.00%	35.00%
Increase in effective tax rate due to GILTI provisions	10.00%
Gross unrecognized tax benefits	$ 27.8	$ 26.9
Unrecognized tax benefits that would impact effective tax rate	$ 17.6
Maximum [Member]
Income Tax Contingency [Line Items]
Percentage of deduction in GILTI Income	50.00%
Gross unrecognized tax benefits balance may decrease within the next twelve months	$ 4.9
Minimum [Member]
Income Tax Contingency [Line Items]
Gross unrecognized tax benefits balance may decrease within the next twelve months	0.0
Internal Revenue Service [Member]
Income Tax Contingency [Line Items]
Additional income tax benefits	$ 0.2

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Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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