Impact of New Accounting Standards - Additional Information (Detail) - USD ($) $ in Millions		6 Months Ended
Jan. 01, 2018	Jun. 30, 2018
Gain on equity securities		$ 2.1
Loss on equity securities		$ 2.6
Accounting Standards Update 2016-01 [Member] \| Accumulated Net Unrealized Investment Losses [Member]
Reclassification from AOCI to retained earnings	$ 6.2

Amount of the cumulative effect on retained earnings net of related income tax effect.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

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