Acquisitions RARE Acquisition - Fair Value Assumptions (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Oct. 21, 2015	Mar. 31, 2015
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability		$ 27,457		$ 27,457			$ 88,581
Business Combination, Contingent Consideration, Liability, Noncurrent		87,770		87,770
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability		26,375	$ 0	26,375	$ 0
RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability	[1]					$ 25,000
Business Combination, Contingent Consideration, Liability, Noncurrent		$ 25,232		25,232
Fund management contracts [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			12 years
Fair Value, Inputs, Level 3 [Member] | Asset Management Contracts | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Inputs, Discount Rate			16.50%
Fair Value Inputs, Long-term AUM Growth Rate			7.00%
Fair Value Inputs, Attrition Rate			(8.00%)
Fair Value, Inputs, Level 3 [Member] | Trade Names | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Input, Projected Cash Flow Growth Rate, Low End of Range		0.00%
Fair Value Input, Projected Cash Flow Growth Rate, High End of Range		10.00%
Fair Value Input, Projected Cash Flow Growth Rate, Average		7.00%
Fair Value Inputs, Discount Rate		16.50%
Fair Value, Inputs, Level 3 [Member] | Fund management contracts [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Input, Projected Cash Flow Growth Rate, Low End of Range		0.00%
Fair Value Input, Projected Cash Flow Growth Rate, High End of Range		10.00%
Fair Value Input, Projected Cash Flow Growth Rate, Average		7.00%
Fair Value Inputs, Discount Rate		16.50%
Performance Fees [Member] | Fair Value, Inputs, Level 3 [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Input, Projected Cash Flow Growth Rate, Low End of Range			0.00%
Fair Value Input, Projected Cash Flow Growth Rate, High End of Range			7.00%
Fair Value Input, Projected Cash Flow Growth Rate, Average			3.00%
Earn-out Payments [Member] | Fair Value, Inputs, Level 3 [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Inputs, Discount Rate			1.90%
Assets Under Management [Member] | Fair Value, Inputs, Level 3 [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Fair Value Input, Projected Cash Flow Growth Rate, Low End of Range			0.00%
Fair Value Input, Projected Cash Flow Growth Rate, High End of Range			14.00%
Fair Value Input, Projected Cash Flow Growth Rate, Average			7.00%
Fair Value Inputs, Discount Rate			6.50%
Fair Value Assumptions, Weighted Average Volatility Rate			20.00%
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
RARE Infrastructure, Ltd [Member]
Business Acquisition, Contingent Consideration [Line Items]
Revenues		$ 8,376

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