Derivatives and Hedging Fair Value of Derivative Assets (Details 1) - Not Designated as Hedging Instrument [Member] - Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Derivative
Derivative Asset, Fair Value, Gross Asset	$ 7,174	$ 3,470
Derivative Asset, Fair Value, Gross Liability	(3,153)	(928)
Derivative Asset	4,021	2,542
Derivative Asset, Not Subject to Master Netting Arrangement	1,088	176
Derivative Asset, Collateral, Obligation to Return Cash, Offset	4,531	2,878
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	9,640	5,596
Foreign Exchange Forward [Member]
Derivative
Derivative Asset, Fair Value, Gross Asset	7,174	3,470
Derivative Asset, Fair Value, Gross Liability	(3,153)	(928)
Derivative Asset	4,021	2,542
Derivative Asset, Not Subject to Master Netting Arrangement	0	0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	4,021	2,542
Forward Contracts [Member]
Derivative
Derivative Asset, Fair Value, Gross Asset		0
Derivative Asset, Fair Value, Gross Liability		0
Derivative Asset		0
Derivative Asset, Not Subject to Master Netting Arrangement		176
Derivative Asset, Collateral, Obligation to Return Cash, Offset		2,878
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		$ 3,054
Investments [Member] | Future [Member]
Derivative
Derivative Asset, Fair Value, Gross Asset	0
Derivative Asset, Fair Value, Gross Liability	0
Derivative Asset	0
Derivative Asset, Not Subject to Master Netting Arrangement	248
Derivative Asset, Collateral, Obligation to Return Cash, Offset	399
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	647
Investments [Member] | Total Return Swap [Member]
Derivative
Derivative Asset, Fair Value, Gross Asset	0
Derivative Asset, Fair Value, Gross Liability	0
Derivative Asset	0
Derivative Asset, Not Subject to Master Netting Arrangement	840
Derivative Asset, Collateral, Obligation to Return Cash, Offset	4,132
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 4,972