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Business Segment Information (Schedule of Financial Information About Business Segments) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Segment Reporting Information [Line Items] |  |
Revenues | $ 405,598 | $ 359,984
Expenses | 274,340 | 251,862
Operating profit (loss) | 131,258 | 108,122
Private Banks [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 122,164 | 112,634
Expenses | 112,202 | 108,550
Operating profit (loss) | 9,962 | 4,084
Investment Advisors [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 99,192 | 88,238
Expenses | 52,453 | 47,539
Operating profit (loss) | 46,739 | 40,699
Institutional Investors [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 85,491 | 77,004
Expenses | 41,249 | 38,828
Operating profit (loss) | 44,242 | 38,176
Investment Managers [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 96,855 | 80,487
Expenses | 63,338 | 52,065
Operating profit (loss) | 33,517 | 28,422
Investments In New Businesses [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 1,896 | 1,621
Expenses | 5,098 | 4,880
Operating profit (loss) | $ (3,202) | $ (3,259)

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