Impairment Charges - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Mar. 31, 2012	Mar. 31, 2012
Impairment [Line Items]
Impairment charges	$ 22.5	$ 32.2
Impairment charge on note receivable	21.4	21.4
Accrued interest	0.8	0.8
Impairment charges on other-than-temporary investment	1.1	10.8
Penson Worldwide Inc [Member] \| Marketable securities [Member]
Impairment [Line Items]
Impairment of marketable securities	$ 10.8	$ 10.8

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.

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale 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.

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