Other Assets - Additional Information (Detail) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Schedule Of Other Assets [Line Items]
Purchase of held to maturity securities	$ 95.8
Record Holdings Pty Limited \| Convertible Preferred Stock
Schedule Of Other Assets [Line Items]
Cost method investment	$ 15.0
Investment percentage	20.00%

Amount of cash outflow through purchase of long-term held-to-maturity securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration