Acquisitions QS Investors Acquisition (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Jun. 30, 2014	Mar. 31, 2013	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Aug. 31, 2016	May 05, 2015	May 30, 2014
Business Acquisition [Line Items]
Revenues				$ 2,886,902	$ 2,660,844	$ 2,819,106
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]			0
QS Investors [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability				4,841	13,749	$ 13,553			$ 13,370
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				8,908
Payments to Acquire Businesses, Gross		$ 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] | 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] | 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				(179)	(196)
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 March 31, 2017, for amounts denominated in currencies other than the U.S. dollar.