Acquisitions (Details) - USD ($) $ in Thousands	Sep. 23, 2016	Sep. 30, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 3,076,700	$ 3,044,807
Ramius Alternative Solutions
Business Acquisition [Line Items]
Assets under management	$ 2,500,000
Cash payment to acquire business	20,500
Contingent consideration payable recorded for acquisition of business	$ 11,900
Goodwill		$ 31,900