Long-Term Debt Interest Rate Swap (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015	Jun. 23, 2014
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Fair Value Disclosure	$ (7,259)		$ (7,259)
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 Instruments in Hedges, Assets, at Fair Value	7,259		7,259		$ 5,462
Treasury Lock [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount						$ 650,000
Other Income [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)	2,772	$ 1,296	1,797	$ 549
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)	(2,772)	$ (1,296)	(1,797)	$ (549)
2.7% Senior Notes [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Fair Value Disclosure	$ (7,259)		$ (7,259)		$ (5,462)