Acquisitions QS Investors Acquisition (Details) £ in Thousands, $ in Thousands		3 Months Ended			9 Months Ended	12 Months Ended
		Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 GBP (£)	Dec. 31, 2016 USD ($)	Aug. 31, 2016 USD ($)	May 05, 2015 USD ($)	Mar. 31, 2015 USD ($)	May 30, 2014 USD ($)
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability						$ 84,585		$ 35,484			$ 110,784
Business Acquisition, Preacquisition Contingency, Amount of Settlement						(22,765)		(6,587)
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]							530,399
Fauchier [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability						0		0			27,117
Payments to Acquire Businesses, Gross				$ 63,433
Business Acquisition, Preacquisition Contingency, Amount of Settlement									$ 6,587	$ 22,765
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]							24,641
QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability						13,749		4,800			$ 13,553	$ 13,370
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					$ 8,949
Payments to Acquire Businesses, Gross		$ 11,000	$ 11,000
Business Acquisition, Preacquisition Contingency, Amount of Settlement									$ 6,587
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High								23,400
Contingent payment due on second anniversary of acquisition | QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High								3,400
Contingent payment due on fourth anniversary of acquisition [Member] | Fauchier [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High | £							£ 20,000
Contingent payment due on fourth anniversary of acquisition [Member] | QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High								$ 20,000
Other changes in Fair Value [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					(5,014)	2,484
Other changes in Fair Value [Member] | Fauchier [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					0	662
Other changes in Fair Value [Member] | QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					138	196
Change in Input Assumptions [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					(39,500)	(33,375)
Change in Input Assumptions [Member] | Fauchier [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability						$ (5,014)
Change in Input Assumptions [Member] | QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					$ (2,500)

[1] Using the applicable exchange rate as of December 31, 2016, for amounts denominated in currencies other than the U.S. dollar.