Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			12 Months Ended
	Jun. 20, 2014	Dec. 12, 2013	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill			$ 3,044,807	$ 3,044,807
Redeemable non controlling interest			$ 13,203	$ 16,504
CPH Capital Fondsmaeglerselskab A/S [Member]
Business Acquisition [Line Items]
Ownership percentage	81.70%		85.40%
Assets under management	$ 3,000,000
Cash paid	64,400
Net contingent consideration payable	9,400
Goodwill	58,100
Definite-lived intangible assets acquired	24,100
Indefinite-lived intangible assets acquired	3,500
Redeemable non controlling interest	$ 16,500
Date of acquisition			Jun. 20, 2014
W.P. Stewart & Co., Ltd. [Member]
Business Acquisition [Line Items]
Assets under management		$ 2,100,000
Net contingent consideration payable		17,100
Goodwill		32,400
Definite-lived intangible assets acquired		14,000
Indefinite-lived intangible assets acquired		$ 7,500
Date of acquisition			Dec. 12, 2013
Cash payment per share on date of acquisition (in dollars per share)		$ 12
Shares outstanding and issued to shareholders transferable contingent value rights (in shares)		4.9
Additional cash payment per share (in dollars per share)		$ 4
Maximum amount equity investments managed by acquiree		$ 5,000,000