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Investments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Investments Schedule [Abstract] |  |  |  |
Realized gain (loss) on trading securities | $ (1.8) | $ 0.2 | $ (1.9) | $ (0.2)

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- References No definition available. + Details
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- Definition Amount of gain (loss) realized from securities classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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