Business Combinations - Summary of Allocation Preliminary Purchase Price (Details) - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill		$ 809,608	$ 660,040
Hermes
Business Acquisition [Line Items]
Cash and Cash Equivalents	$ 175,800
Other Current Assets	53,700
Goodwill	154,900
Intangible Assets	276,200
Other Long-Term Assets	35,100
Less: Long-Term Deferred Tax Liability, net	(19,500)
Less: Liabilities Assumed	(162,300)
Less: Fair Value of Redeemable Noncontrolling Interest in Subsidiary	(169,600)
Total Purchase Price Consideration	344,300
Receivables	31,900
Property and Equipment, net	11,200
Accrued Compensation and Benefits	130,300
Hermes | Trade Name
Business Acquisition [Line Items]
Indefinite-lived intangible assets	49,900
Hermes | Investment Advisory Contracts
Business Acquisition [Line Items]
Indefinite-lived intangible assets	132,700
Hermes | Customer Relationships
Business Acquisition [Line Items]
Customer relationships	$ 93,600
Weighted-average useful life	8 years 5 months