Short-Term Borrowings and Long-Term Debt Interest Rate Swap - Revolving Credit Facility (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Jun. 23, 2014
Line of Credit Facility [Line Items]
Derivative, Term of Contract		4 years 245 days
Revolving Credit Facility [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Fixed Interest Rate	2.30%
Derivative, Notional Amount	$ 500,000
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		$ 38,569	$ 34,857
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Notional Amount					$ 250,000
Other Nonoperating Income (Expense) [Member] | Cash Flow Hedging [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative	$ 3,662	3,662	0
Interest Expense [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative			$ 0	$ 0
Interest Expense [Member] | Cash Flow Hedging [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative		$ 764