Acquisitions Martin Currie Acquisition (Details) £ in Thousands, $ in Thousands		3 Months Ended		6 Months Ended	12 Months Ended
		Dec. 31, 2014 GBP (£)	Dec. 31, 2014 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2016 GBP (£)	Sep. 30, 2016 USD ($)		Mar. 31, 2015 USD ($)	Oct. 01, 2014 USD ($)
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Current							$ 11,315
Business Combination, Contingent Consideration, Liability					$ 84,585		52,053		$ 110,784
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]						557,929
Martin Currie [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Current							5,568
Business Combination, Contingent Consideration, Liability					41,222		19,797		$ 70,114	$ 75,211
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ 21,425
Payments to Acquire Businesses, Gross		£ 125,000	$ 202,577
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High						£ 325,000	$ 421,840	[1]
Change in Input Assumptions [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(25,000)	(33,375)
Change in Input Assumptions [Member] | Martin Currie [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(18,000)	(28,361)
Other changes in Fair Value [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(2,945)	2,484
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				$ (3,425)	$ (531)

[1] (1)Using the applicable exchange rate as of September 30, 2016, for amounts denominated in currencies other than the U.S. dollar.