Income Taxes - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Dec. 31, 2017	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Effective rate (as a percent)		22.30%
Discrete tax benefit		$ 0.6
Discrete tax benefit from stock compensation windfall		0.1
Discrete tax benefit related to re-measurement of deferred taxes		$ 0.5
Reduction in income tax expense due to Tax Cuts and Jobs Act of 2017	$ (9.2)

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

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Balance Type:	na
Period Type:	duration