Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Mar. 31, 2018
Other Assets [Member]
Derivative
Amount Net for Fair Value of Derivative Assets and (Liabilities)		$ 3,866	$ 4,904
Other Liabilities [Member]
Derivative
Amount Net for Fair Value of Derivative Assets and (Liabilities)		9,326	$ 6,446
Foreign Exchange Forward [Member]
Derivative
Derivative, Notional Amount		417,807
Derivative, Average Remaining Maturity	7 months
Future [Member]
Derivative
Derivative, Notional Amount		112,117
Derivative, Average Remaining Maturity	3 months
Total Return Swap Expiring in May 2019_2 [Member]
Derivative
Derivative, Notional Amount		5,354
Aggregate Counterparty Investment in ETF		5,573
Derivative, Fixed Interest Rate	1.60%
Total Return Swap Expiring in July 2019 [Member]
Derivative
Derivative, Notional Amount		15,819
Aggregate Counterparty Investment in ETF		17,094
Derivative, Fixed Interest Rate	1.60%
Total Return Swap Expiring in November 2019 [Member] [Member]
Derivative
Derivative, Notional Amount		10,073
Aggregate Counterparty Investment in ETF		9,886
Total Return Swap Expiring in October 2019 [Member] [Domain]
Derivative
Derivative, Notional Amount		10,073
Aggregate Counterparty Investment in ETF		10,000
Total Return Swap [Member]
Derivative
Derivative, Notional Amount		41,319
Aggregate Counterparty Investment in ETF		42,553
Derivative Financial Instruments, Assets [Member] | Future [Member]
Derivative
Derivative, Notional Amount		$ 41,522