This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 35
-Paragraph 32
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
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Investments In Unconsolidated Subsidiaries - Additional information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Global Investment Management [Member]
Schedule of Equity Method Investments [Line Items]
Non-cash write downs of investments			$ 3.6
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	$ 86.8	$ 98.1	$ 140.6
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%