Short-Term Borrowings and Long-Term Debt Interest Rate Swap - 2.7% Senior Notes due July 2019 (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 16, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jul. 26, 2017	Jun. 06, 2017	Jun. 23, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount						$ 23,096	$ 20,253
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Loss on Derivative		$ (11,955)	$ (11,443)	$ (19,447)	$ (23,580)
Derivative, Gain on Derivative		6,317	2,190	10,819	15,185
Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortization of Deferred Hedge Gains			$ 451		$ 902
2.7% Senior Notes [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount								$ 250,000
Derivative, Gain on Derivative	$ 6,500
Amortization of Deferred Hedge Gains		$ 451		$ 902