Fair Value - Additional Information (Details)	3 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) investment	Dec. 31, 2016 USD ($) investment acquisition $ / shares	Dec. 31, 2015 USD ($) investment acquisition	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of private equity investment		$ 40,400,000	$ 32,000,000
Number of VIEs consolidated | investment	6
Number of hedge funds consolidated | investment		1
Number of private securities that went public | investment	1
Transfers out of level 3	$ 23,600,000
Changes in estimates		$ 21,482,000	7,211,000
Contingent payment arrangements		11,893,000	0	$ 9,365,000
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent payment arrangements		$ 17,589,000	31,399,000
Luxembourg Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of VIEs consolidated | investment		7
Private Equity Investment Venture Capital Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investment		$ 4,900,000	$ 6,500,000
Contingent Payment Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of Businesses Acquired | acquisition		3	3
Contingent Payment Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in estimates			$ 7,200,000
Contingent payment arrangements		$ 17,600,000	$ 31,400,000
Contingent Payment Arrangements [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AUM growth rates weighted average		18.00%	46.00%
Revenue growth rate			43.00%
Contingent Payment Arrangements [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revenue growth rate		4.00%
Discount rate		1.40%	3.00%
Contingent Payment Arrangements [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revenue growth rate		31.00%
Discount rate		6.40%	6.40%
Cost-method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of private equity investments | investment			1
Fair value of private equity investment			$ 10,200,000
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent payment arrangements		$ 17,589,000	$ 31,399,000
Fair Value, Inputs, Level 3 [Member] | Luxembourg Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of VIEs consolidated | investment		5
Fair value of investment		$ 5,700,000
2010 Acquisition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in estimates		(2,200,000)
2013 Acquisition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in estimates		$ (19,300,000)
Additional amount per share shareholders are entitled to if the assets under management exceed the threshold (in dollars per unit) | $ / shares		$ 4
Assets under management threshold		$ 5,000,000,000