Fair Value (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) investment $ / shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) investment acquisition	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) investment acquisition
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Private equity investments measured at cost	$ 31,600,000		$ 31,600,000		$ 32,000,000
Number of private equity investments measured using practical expedient | investment			1		1
Number of variable interest entities consolidated | investment	2		2
Number of private securities that went public | investment	1
Amount transferred from Level 3 to Level 2	$ 23,600,000
Changes in estimates	(21,483,000)	$ 0	$ (21,483,000)	$ 0
Assets measured at fair value for impairment on a nonrecurring basis	0		0		$ 0
Liabilities measured at fair value for impairment on a nonrecurring basis	0		$ 0		$ 0
Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of acquisitions | acquisition			3		3
Private Equity Investment Energy Fund
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of investments	4,800,000		$ 4,800,000		$ 6,500,000
Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent payment arrangements	18,017,000		18,017,000		31,399,000
Recurring | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent payment arrangements	18,000,000		$ 18,000,000		$ 31,400,000
Weighted Average | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
AUM growth rate			18.00%		46.00%
Revenue growth rate					43.00%
Minimum | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Revenue growth rate			4.00%
Discount rate			1.40%		3.00%
Maximum | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Revenue growth rate			31.00%
Discount rate			6.40%		6.40%
Level 3 | Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent payment arrangements	$ 18,017,000		$ 18,017,000		$ 31,399,000
Luxembourg Funds
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of variable interest entities consolidated | investment	4		4
Luxembourg Funds | Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of variable interest entities consolidated | investment	3		3
Fair value of investments	$ 2,800,000		$ 2,800,000
Cost-method Investments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of private equity investments | investment					1
Private equity investments measured at cost					$ 10,200,000
2010 Acquisition
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Changes in estimates	$ 2,200,000
2013 Acquisition
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Additional amount per share shareholders are entitled to if the assets under management exceed the threshold (in dollars per share) | $ / shares	$ 4
Assets under management threshold	$ 5,000,000,000
Changes in estimates	$ 19,300,000