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Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 Securities | Jun. 30, 2012 | Mar. 31, 2012 | Jun. 30, 2013 Securities | Jun. 30, 2012 | Dec. 31, 2012 Securities
Investment [Line Items] |  |  |  |  |  |
Number of securities accounted for gross unrealized losses | 158 |  |  | 158 |  | 49
Cost basis of securities at disposal | $ 5.0 | $ 0.9 |  | $ 5.0 | $ 20.0 |
Realized gains on sale of equity securities | 0.6 | 0.1 |  | 0.6 | 1.9 |
Impairment losses recognized |  | 0 | 0 |  |  |
Equity Securities [Member] |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |
Impairment losses recognized | $ 1.9 |  |  | $ 1.9 |  |

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- Definition For any sales of securities categorized as available-for-sale, this item represents the carrying amount of the sold security. + References No definition available. + Details
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- Definition Number of Securities Accounted For Gross Unrealized Losses + References No definition available. + Details
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- Details
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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26805-111562 + Details
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- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560 + Details
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