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Business Segments - Segment Reporting, Reconciliation of Revenues, Operating Income and Assets (Parenthetical) (Detail) (USD $)
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3 Months Ended | 12 Months Ended | |||||||||
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Dec. 31, 2014
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Sep. 30, 2014
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Jun. 30, 2014
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Mar. 31, 2014
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Dec. 31, 2013
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Sep. 30, 2013
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Jun. 30, 2013
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Mar. 31, 2013
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Segment Reporting Information [Line Items] | |||||||||||
| Total revenues | $ 450,865,000 | $ 415,151,000 | $ 460,089,000 | $ 434,682,000 | $ 436,764,000 | $ 423,058,000 | $ 410,693,000 | $ 479,971,000 | $ 1,760,787,000 | $ 1,750,486,000 | $ 1,960,518,000 |
| Europe Private Capital Segment [Member] | |||||||||||
| Segment Reporting Information [Line Items] | |||||||||||
| Goodwill | 25,300,000 | 25,300,000 | 25,300,000 | 25,300,000 | |||||||
| United States [Member] | |||||||||||
| Segment Reporting Information [Line Items] | |||||||||||
| Total revenues | 1,400,000,000 | 1,100,000,000 | 1,100,000,000 | ||||||||
| Long-lived assets attributable to the United States | $ 17,300,000,000 | $ 15,300,000,000 | $ 17,300,000,000 | $ 15,300,000,000 | |||||||