The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Goodwill and Other Intangibles - Narratives (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets, Net
Goodwill	$ 645,736		$ 643,960
Amortization of intangible assets	38,800	$ 37,700
Owned Real Estate
Finite-Lived Intangible Assets, Net
Goodwill foreign currency translation adjustments	1,700
Goodwill	582,100		580,400
Investment Management
Finite-Lived Intangible Assets, Net
Goodwill	$ 63,600		$ 63,600
Minimum
Finite-Lived Intangible Assets, Net
Finite lived intangible assets useful life	1 year
Maximum
Finite-Lived Intangible Assets, Net
Finite lived intangible assets useful life	40 years
Maximum \| Below-market ground lease
Finite-Lived Intangible Assets, Net
Finite lived intangible assets useful life	99 years