Commitments and Contingencies Commitments and Contingencies related to Acquisitions (Details) £ in Thousands, AUD in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)	Oct. 21, 2015 AUD	Oct. 21, 2015 USD ($)		May. 05, 2015 GBP (£)	May. 05, 2015 USD ($)	Mar. 31, 2015 USD ($)	Oct. 01, 2014 USD ($)		May. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Mar. 13, 2013 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							$ 90,464						$ 110,784				$ 29,553
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability							27,457						88,581
Business Combination, Contingent Consideration, Liability, Current							2,694
Business Combination, Contingent Consideration, Liability, Noncurrent							87,770
Business Acquisition, Preacquisition Contingency, Amount of Settlement							(22,765)
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability		$ 26,375	$ 0	$ 26,375	$ 0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]						617,855
RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							25,232		$ 25,000	[2]			0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability	[3]								25,000
Business Combination, Contingent Consideration, Liability, Current							0
Business Combination, Contingent Consideration, Liability, Noncurrent							25,232
Business Acquisition, Preacquisition Contingency, Amount of Settlement							0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High								AUD 106,000	77,253	[1]
Martin Currie [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							49,078						70,114	$ 75,211			0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability							0							75,211	[3]
Business Combination, Contingent Consideration, Liability, Current							0
Business Combination, Contingent Consideration, Liability, Noncurrent							49,078
Business Acquisition, Preacquisition Contingency, Amount of Settlement							0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(21,036)
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High						£ 325,000	478,687							$ 478,687	[1]
PK Investments [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							2,457						0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability	[3]								2,457
Business Combination, Contingent Consideration, Liability, Current							0
Business Combination, Contingent Consideration, Liability, Noncurrent							2,457
Business Acquisition, Preacquisition Contingency, Amount of Settlement							0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]								$ 2,457
QS Investors [Domain]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							13,697						13,553			$ 13,370	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability							0									13,370
Business Combination, Contingent Consideration, Liability, Current							2,694
Business Combination, Contingent Consideration, Liability, Noncurrent							11,003
Business Acquisition, Preacquisition Contingency, Amount of Settlement							0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]															$ 30,000
Fauchier [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability							0						27,117				$ 29,553	$ 21,566
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability							0						$ 0
Business Combination, Contingent Consideration, Liability, Current							0
Business Combination, Contingent Consideration, Liability, Noncurrent							$ 0
Business Acquisition, Preacquisition Contingency, Amount of Settlement											£ 15,000	$ (22,765)
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(27,117)
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	[1]																	$ 29,458
Other changes in Fair Value [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				1,363	(7,350)
Other changes in Fair Value [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				232
Other changes in Fair Value [Member] | Martin Currie [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				325	(5,097)
Other changes in Fair Value [Member] | PK Investments [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				0
Other changes in Fair Value [Member] | QS Investors [Domain]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				144	183
Other changes in Fair Value [Member] | Fauchier [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				662	(2,436)
Change in Input Assumptions [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(26,375)	$ 0
Change in Input Assumptions [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				0
Change in Input Assumptions [Member] | Martin Currie [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				(21,361)
Change in Input Assumptions [Member] | PK Investments [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				0
Change in Input Assumptions [Member] | QS Investors [Domain]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				0
Change in Input Assumptions [Member] | Fauchier [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ (5,014)

[1] Using the applicable exchange rate as of December 31, 2015 for amounts denominated in currencies other than the U.S. dollar.

[2] (1)Subject to prospective adjustments, including for amounts ultimately realized and adjustments provided for in the share purchase agreement.

[3] Using the applicable exchange rate on the date of acquisition for amounts denominated in currencies other than the U.S. dollar.