Short-Term Borrowings and Long-Term Debt Interest Rate Swap - 2.7% Senior Notes due July 2019 (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 16, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Jun. 26, 2014	Jun. 23, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount					$ 553
Debt Instrument, Basis Spread on Variable Rate		1.25%
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Gain on Derivative		$ 19,308	$ 25,414
Derivative, Loss on Derivative		(38,569)	(34,857)
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		1,804
Interest Expense [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Gain on Derivative		0	5,710	$ 5,462
Derivative, Loss on Derivative			0	0
Other Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)			(2,137)	(5,462)
Other Income [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)			$ 2,137	$ 5,462
2.7% Senior Notes [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount		$ 250
US Treasury Interest Rate [Member] | 2.7% Senior Notes [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.20%