v3.8.0.1

Income Taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Of Unrecognized Tax Benefits [Line Items]
Beginning Balance	$ 39.8	$ 15.6	$ 7.6
Increases related to prior year tax positions			2.6
Increases related to current year tax positions	3.3	32.6	5.4
Decreases related to prior year tax positions	(14.9)	(8.4)
Decrease related to Tax Cuts and Jobs Act of 2017	(5.4)
Ending Balance	22.8	$ 39.8	$ 15.6
Unrecognized Tax Benefits, Income Tax Penalties Expense	$ 0.0

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- Definition

Reconciliation Of Unrecognized Tax Benefits [Line Items]

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Unrecognized Tax Benefits, Decrease Related To TCJA

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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Amount of expense for penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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-Name Accounting Standards Codification
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-Section 50
-Paragraph 15A
-Subparagraph (a)(2)
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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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