Derivatives and Hedging (Tables)

12 Months Ended

Mar. 31, 2018

Derivative Instruments and Hedging Activities Disclosures [Line Items]

Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]

Transaction Date	Expiration Date	Aggregate Counterparty Initial Investment in ETF		Floating Rate	Aggregate Notional Amount as of March 31, 2018
October 10, 2017	April 2018	$	5,290	Three-month LIBOR plus 1.6%	$	6,064
July 26, 2017	July 2018	23,096		Three-month LIBOR plus 1.6%	22,156
June 6, 2017	June 2018	20,253		Three-month LIBOR plus 1.35%	21,851
		$	48,639		$	50,071

Schedule of Derivative Assets at Fair Value [Table Text Block]

								Gross amounts not offset in the Balance Sheet
	Gross amounts of recognized assets		Gross amounts offset in the Balance Sheet			Net amount of derivative assets presented in the Balance Sheet		Financial instruments		Cash collateral		Net amount as of March 31, 2017
Derivative instruments not designated as hedging instruments
Currency forward contracts	$	3,470	$	(928	)	$	2,542	$	—	$	—	$	2,542
Futures contracts relating to seed capital investments	—		—			—		176		2,878		3,054
Total derivative instruments not designated as hedging instruments	$	3,470	$	(928	)	$	2,542	$	176	$	2,878	$	5,596

								Gross amounts not offset in the Balance Sheet
	Gross amounts of recognized assets		Gross amounts offset in the Balance Sheet			Net amount of derivative assets presented in the Balance Sheet		Financial instruments		Cash collateral		Net amount as of March 31, 2018
Derivative instruments not designated as hedging instruments
Currency forward contracts	$	7,997	$	(3,177	)	$	4,820	$	—	$	—	$	4,820
Total return swaps	—		—			—		84		1,283		1,367
Total derivative instruments not designated as hedging instruments	$	7,997	$	(3,177	)	$	4,820	$	84	$	1,283	$	6,187

Schedule of Derivative Liabilities at Fair Value [Table Text Block]

									Gross amounts not offset in the Balance Sheet
	Gross amounts of recognized liabilities			Gross amounts offset in the Balance Sheet		Net amount of derivative liabilities presented in the Balance Sheet			Financial instruments			Cash collateral		Net amount as of March 31, 2018
Derivative instruments not designated as hedging instruments
Currency forward contracts	$	(532	)	$	223	$	(309	)	$	—		$	—	$	(309	)
Futures contracts relating to:
Seed capital investments	—			—		—			(2,875		)	9,214		6,339
Total return swaps	—			—		—			(1,029		)	3,201		2,172
Total futures contracts	—			—		—			(3,904		)	12,415		8,511
Total return swaps	—			—		—			(2,233		)	5,637		3,404
Total derivative instruments not designated as hedging instruments	$	(532	)	$	223	$	(309	)	$	(6,137	)	$	18,052	$	11,606

									Gross amounts not offset in the Balance Sheet
	Gross amounts of recognized liabilities			Gross amounts offset in the Balance Sheet		Net amount of derivative liabilities presented in the Balance Sheet			Financial instruments			Cash collateral		Net amount as of March 31, 2017
Derivative instruments not designated as hedging instruments
Currency forward contracts	$	(3,641	)	$	751	$	(2,890	)	$	—		$	—	$	(2,890	)
Futures contracts relating to seed capital investments	—			—		—			(1,632		)	4,155		2,523
Total derivative instruments not designated as hedging instruments	$	(3,641	)	$	751	$	(2,890	)	$	(1,632	)	$	4,155	$	(367	)

Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance

		Years Ended March 31,
		2018					2017					2016
	Income Statement Classification	Gains		Losses			Gains		Losses			Gains		Losses
Derivatives not designated as hedging instruments
Currency forward contracts relating to:
Operating activities	Other expense	$	13,880	$	(6,774	)	$	14,524	$	(13,098	)	$	7,887	$	(19,547	)
Seed capital investments	Other non-operating income (expense)	494		(2,459		)	2,681		(2,443		)	547		(1,611		)
Other non-operating activities (1)	Other non-operating income (expense)	—		—			—		—			—		(4,493		)
Futures contracts relating to:
Seed capital investments	Other non-operating income (expense)	222		(24,025		)	2,103		(18,602		)	11,270		(9,206		)
Total return swaps	Other non-operating income (expense)	90		(8,721		)	—		—			—		—
Total return swaps	Other non-operating income (expense)	2,247		(1,142		)	—		—			—		—
Total gain (loss) from derivatives not designated as hedging instruments		16,933		(43,121		)	19,308		(34,143		)	19,704		(34,857		)
Derivative designated as a fair value hedge (See Note 6)
Interest rate swap	Interest expense	—		—			—		—			5,710		—
Derivative designated as a cash flow hedge (See Note 6)
Interest rate swap (termination)	Other non-operating income (expense)	—		—			—		(3,662		)	—		—
Interest rate swap	Interest expense	—		—			—		(764		)	—		—
Total		$	16,933	$	(43,121	)	$	19,308	$	(38,569	)	$	25,414	$	(34,857	)

(1) Relates to a currency forward executed in August 2015 and closed in October 2015 in connection with the October 2015 acquisition of RARE Infrastructure.