Acquisitions Martin Currie Acquisition (Details) £ in Thousands, $ in Thousands	12 Months Ended
	Mar. 31, 2017 USD ($)		Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Mar. 31, 2015 GBP (£)	Mar. 31, 2017 GBP (£)	Oct. 01, 2014 USD ($)
Business Acquisition [Line Items]
Revenues	$ 2,886,902		$ 2,660,844	$ 2,819,106
Martin Currie [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Current	12,018
Business Combination, Contingent Consideration, Liability	12,018		41,222	70,114			$ 75,211
Payments to Acquire Businesses, Gross				$ 202,577	£ 125,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	407,403	[1]				£ 325,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	(29,204)
Change in Input Assumptions [Member] | Martin Currie [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	(25,000)		(28,361)
Other changes in Fair Value [Member] | Martin Currie [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ (4,204)		$ (531)

[1] Using the applicable exchange rate as of March 31, 2017, for amounts denominated in currencies other than the U.S. dollar.