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Investments In Unconsolidated Subsidiaries - Additional information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Investment management, property management, brokerage and other professional services [Member] | Global Investment Management [Member] |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |
Revenues from unconsolidated subsidiaries | $ 100.3 | $ 86.8 | $ 98.1
Maximum [Member] | Global Investment Management [Member] |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |
Equity method investments in unconsolidated subsidiaries, variations in ownership percentage | 5.00% |  |
Maximum [Member] | Development Services [Member] |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |
Equity method investments in unconsolidated subsidiaries, variations in ownership percentage | 10.00% |  |
Maximum [Member] | Other [Member] |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |
Equity method investments in unconsolidated subsidiaries, variations in ownership percentage | 50.00% |  |

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- Definition Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates. + 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 210.5-03.1(e)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07.1(c)) -URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999 + Details
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