Significant Accounting Policies Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt, Fair Value	$ 2,264,867	$ 1,773,852
Proprietary Funds [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Proprietary Funds [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Partnership Interest [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	3.00%