Derivatives and Hedging Gains and (Losses) of Derivative Instruments (Details) - Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain on Derivative	$ 6,238	$ 13,615
Derivative, Loss on Derivative	(9,228)	(12,757)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	6,238	13,615
Derivative Instruments Not Designated as Hedging Instruments, Loss	(9,228)	(12,230)
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	0	0
Derivative Instruments Not Designated as Hedging Instruments, Loss	(107)	0
Not Designated as Hedging Instrument [Member] \| Forward Contracts [Member] \| Other Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	4,712	10,530
Derivative Instruments Not Designated as Hedging Instruments, Loss	(2,572)	7,983
Not Designated as Hedging Instrument [Member] \| Proprietary Funds [Member] \| Forward Contracts [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	411	1,334
Derivative Instruments Not Designated as Hedging Instruments, Loss	(1,049)	856
Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain on Derivative	0	0
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swap [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Loss on Derivative	0	(527)
Investments [Member] \| Not Designated as Hedging Instrument [Member] \| Future [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	848	1,751
Derivative Instruments Not Designated as Hedging Instruments, Loss	(5,500)	(3,391)
Derivative Financial Instruments, Assets [Member] \| Not Designated as Hedging Instrument [Member] \| Future [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain	267	0
Derivative Instruments Not Designated as Hedging Instruments, Loss	$ 0	$ 0

Amount of increase in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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