Short-Term Borrowings and Long-Term Debt Interest Rate Swap - Revolving Credit Facility (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Line of Credit Facility [Line Items]
Derivative, Term of Contract	4 years 245 days
Interest Rate Swap [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Derivative, Fixed Interest Rate				2.30%
Derivative, Notional Amount				$ 500,000
Derivative, Term of Contract	4 years 245 days
Derivative Liability, Not Subject to Master Netting Arrangement			$ (3,662)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax			(2,249)
Deferred Tax Assets, Hedging Transactions			1,413
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative		$ 30,141	30,447
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Expense [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative		$ 0	$ 764